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CBSE Class 12 Science Board Exam: Subject-wise common mistakes noted by board examiners

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These silly and common mistakes in the CBSE Class 12 Physics, Chemistry and Biology papers as listed by experienced board examiners make students lose a lot of marks!

The CBSE Class 12 board exams will begin on February 15, 2019, and end on April 3, 2019. There is barely a month left for the exams to start and most students are revising the syllabus and practicing mock tests and sample papers. We have for you a list of the common mistakes students lose marks in the CBSE Class 12 board exam, as noted by experiences board examiners of the respective subjects.

Take care you don’t make these silly errors as no amount of preparation can decide whether you will slip up at exam time!

Here are the dates for the main CBSE Class 12 Science stream exams:

  • Physics: March 5, 2019
  • Chemistry: March 12, 2019
  • Biology: March 15, 2019
  • Maths: March 18, 2019

Board examiner points out common mistakes in CBSE Class 12 Physics Board Exam

India Today got talking to Shampa Chakraborty, senior Physics teacher at Hariyana Vidya Mandir school, Kolkata, with 20 years of teaching experience, and an experienced Board examiner, who pointed out the silly errors students make which Board examiners cut marks for. Most of these errors have absolutely nothing to do with your knowledge of the subject and can easily be avoided.

Here are the common errors you can easily avoid in your CBSE Class 12 Physics paper:

1. The answer length Class 12 CBSE Physics Board exam should be in accordance to the marks provided for the question. A question of 1 mark should not be answered in half a page or a whole page.

2. Even good students at times do not write the formula when doing numericals. However, marks are allotted for the formula itself and not writing the formula will make you lose marks.

3. Students often flip the numerator and denominator in formulae by mistake. This makes sure that the entire working of the numerical problem is incorrect and you get absolutely no marks for the answer.

4. An extremely common mistake students make in the Class 12 CBSE Physics Board exam is in the formula for finding capacitance in series. The formula is: 1/c= 1/c1 + 1/c2. However, students commonly write: c= 1/c1 + 1/c2

5. In value-based questions, which are generally of 2 marks, students tend to write only one sentence. They ought to write 3-4 sentences in order to get full marks.

6. For questions where diagrams are asked for, students should label them properly and preferably, in pencil.

7. In the Class 12 CBSE Physics Board exam, most questions have several parts in it, and each part is allocated some marks. Students often tend to overlook or miss out on a small part of the question, thus losing anything from half a mark to 3 marks for the same.

8. In questions of 1 mark which are asking for a “yes” or “no” answer, students should write thereason for the “yes” or “no” as well in order to get full marks. Most of the time, such questions are allocated a half mark each for the two parts of the answer.

9. Students should make sure they write the correct question number for the answer they are writing. Any mistake here means they would lose the entire marks even if their answer is correct.

10. Students often re-write certain questions. In that case, they MUST make sure that you strike out the first answer. If that isn’t done, CBSE rules ask examiners to accept the first attempt and ignore the second attempt.

Board examiner points out common mistakes in CBSE Class 12 Chemistry Board Exam

India Today Education got talking to Joyoti Chaudhuri, higher secondary Chemistry teacher with 22 years of CBSE teaching experience, and several years of experience as a board examiner and Head Examiner of Chemistry for AISSE.

She pointed out the silly errors students make in the three sections of Physical, Organic and Inorganic Chemistry, explaining the section-wise marks allotment in certain question patterns. This will help students understand where exactly they have a chance of losing marks at the hands of the Board examiner. Most of these errors have absolutely nothing to do with your knowledge of the subject and can easily be avoided.

Here are the common errors you can easily avoid in your CBSE Class 12 Chemistry paper:

Physical Chemistry

1. In a numerical, half mark or 1 mark each is assigned to:

  • writing the working formula
  • posting data in working formula
  • correct numerical value
  • proper unit

Common mistakes made are:

  • they do not write working formula
  • they do not post data in working formula
  • calculation error
  • they do not check compatibility of all units, i.e. all units of each data should be either in SI or CGS units

2. All laws should be written as it was stated. Students reframe the statement or only write the mathematical expression. Please note marks are allotted to the statement of law only.

3. While plotting a graph, both the independent and dependent variables must be written. Students often plot the graph and do not write the variables. Be cautious.

4. Reason based questions must be answered in two points: (i) cause (ii) consequence. Though these questions carry one mark each, two key points are expected from students. Most of the time students write only one point.

Inorganic Chemistry

Common mistakes in the four key areas from which questions are set:

1. Stuctures

lone pair of electrons, if present, are not shown

if structure/geometry of a molecule is asked, students only draw it and do not write it

when asked to draw the structure of molecule, students only write it, and do not draw

2. Equations

Balancing equations is a MUST

Often, if the question is asking about the observation of a reaction then students mistakenly write the equation and vice versa

3. Reason based questions: Same errors as in physical chemistry. If the consequence is due to a phenomenon such as Lanthanide contraction, or inert pair effect, these terms must be mentioned.

4. Principle involved in a process: Students often write the process or steps involved but do not mention the principle behind the process.

Organic Chemistry

1. IUPAC nomenclature:

Students commonly make mistakes in writing the suffix, for instance –ol should not look like -al

Another mistake made is in identifying the substituted alkyl group

2. Distinction between pair of organic compounds:

Correct reagent needs to be written with corresponding observation. Mistake lies in writing the name of the test like iodoform test and not writing the reagent i.e. NaOH and I2

Another common mistake is not writing which compound is responding to the test though the observation is given

3. Equation/name reaction: Answer must correspond to the question; you need to check whether name or structure/formula is asked for in the question.

4. Conversion: Reagents involved in each step must be shown.

5. Mechanism:

Arrows showing the electron transfer must be shown

Type of reaction involved must be written (eg: nucleophilic substitution)

6. Reason based answers must include two key points, i.e. cause and consequence.

Finally like in all subjects, word limit must be maintained. Keywords should be highlighted. Try to solve the entire paper first rather than putting too much time in solving one question; time management is important.

Board examiner points out common mistakes in CBSE Class 12 Biology Board Exam

As we are moving into digital education even more, there are a number of CDs available to understand the concepts even better via video. You can look up the different topics online as well to get a number of digital concepts to clear your concepts in Biology. You will be able to explain various topics almost in your own words if you are in a rush and need to complete your syllabus quickly.

But for CBSE Boards, reading your Biology NCERT book cover-to-cover is enough to score more than 90 per cent. If you have no plans on building a career in the field of Biology, you can score well even by mugging up this theoretical subject.

India Today Education spoke to DPS Ruby Park (Kolkata) Biology teacher Piyali Chatterjee Sen, the Head Board examiner of Biology for six years, with 25 years of teaching experience, about the common mistakes students make in Boards for which they lose marks.

Here are the common errors you can easily avoid in your CBSE Class 12 Biology paper:

1. Not utilizing the reading time fruitfully

Fifteen minutes is enough time to read the CBSE Class 12 Biology question-paper thoroughly and plan out strategies to frame answers in the best possible way.

Also, concentrated reading will result in vivid scrutiny of all the part questions or sub-questions of a long question and thereby minimize errors and question drops.

2. Writing in paragraph form

Students should abstain from writing in paragraph form. Answers should always be written in point-wise manner, using bullets or arrows.

Also, students should underline/highlight the important terms used, thereby facilitating the examiner to evaluate in a better manner and fairly.

Long answers should be preferably written in schematic or flowchart form.

3. Avoiding pictorial/diagrammatic illustrations

CBSE Biology and the subject of Bio-science prefers the use of diagrams at various levels. 2-mark, 3-mark and 5-mark questions should be accompanied by diagrams wherever possible as CBSE gives importance to diagrams.

Diagrams have to be labeled. Students should preferably use pencil for drawing and labeling. Labels should all be on the right side of the diagram.

4. Forgetting to cite examples

The NCERT book has several examples of types, patterns, flora and fauna for CBSE Class 12 Biology. While answering, those examples need to be given as the marking scheme has marks allotted for the same.

5. Tendency of writing more than required

CBSE puts a lot of stress on writing to the point and not exceeding word limit.

If two marks are allotted, only two points have to be mentioned.

Writing excess will not only result in loss of time, but might also lead to the deduction of marks awarded to the answer.

6. Haphazard pattern of answering

Writing answers serially is the ideal approach. However, many students tend to jump from one section to another, without completing that particular section. This can irritate the examiner leading to improper marking.

7. Tendency of writing till the stroke of the bell

A combined effect of excess writing, stress and fear leads to improper time management.

By writing till the end, the student fails to conserve time for revision or for pondering on HOTS questions.

8. Improper detailing of value-based questions

Just stating facts in this section is not justified for the CBSE Class 12 Biology Board exam.

Answers to such questions need to have a touch of life skills or values.

9. Neglecting NCERT text material

Students have a tendency to avoid details and examples of the NCERT book and prefer citing information from reference books. Little do they know that the marking scheme sent by the board is 100 per cent based on NCERT, and Board examiners have to adhere to the marking scheme while correcting Board papers.

Thorough reading of the NCERT is mandatory to succeed in CBSE Board exams.

Board examiner points out common mistakes in CBSE Class 12 Mathematics Board Exam

India Today Education spoke to Hariyana Vidya Mandir (Kolkata) Mathematics teacher Debjani Kar, an experienced Board Examiner for several years, with almost 20 years of teaching experience, about the common mistakes students make in the Class 12 CBSE Mathematics Board exam for which they lose out on getting a full 100 per cent.

Read: CBSE brings change in board exam! Class 10 Maths board exams to have two levels from 2020

Here are a few tips from the experienced Board Examiner to get full marks on your Class 12 CBSE Mathematics paper:

1. For the sums of Matrix Elementary Operation, do not change rows and columns together in the same sum. For row transformation, change only row, and for column transformation, change only column.

2. In the Determinant sums, to get full marks, students must use the properties of determinant.

3. For sums of Indefinite Integral, students must write the constant of integration.

4. For Linear Programming problems, proper shading of the feasible region is very important. If the region is unbounded, don’t forget to draw the kink line.

5. In the sums of Vector Algebra and 3D-Geometry, do not forget to give vector sign.

6. In 1-mark questions, always try to write the correct answer of the sum. If steps are correct and answer is wrong, step marking or point marking becomes very difficult.

7. Students often forget to write this when solving such problems in their Class 12 CBSE Mathematics paper:

8. In such questions, remember not to take log on both sides!

So, keep your fingers crossed and keep practicing your sample papers and previous years’ papers! Prepare well, and make sure you do not make these silly errors in your exam hall to avoid losing marks even when you know the answers. All the best!


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