Previous year questions are the best investment of your study time. For acids, bases and salts (Class 7), the same concepts cycle through CBSE, NEET, and JEE papers with small tweaks. We will walk through a representative PYQ below.
Question
Blue litmus turns red in solution X. Is X an acid or a base? If X is 0.001 M HCl, find its pH.
(Adapted from recent board and entrance exam patterns on acids, bases and salts (Class 7).)
Solution — Step by Step
This PYQ tests your grip on natural indicators (litmus, turmeric, china rose), sour vs bitter tastes. Before solving, name the concept — that alone earns method marks in board exams.
Write down every number with its unit. Circle what is asked. Skipping this step is why students misread easy PYQs as “tricky”.
Use the standard formula or definition relevant to acids, bases and salts (Class 7). The examiner is not trying to trap you — they want to see you execute the textbook method cleanly.
Acidic; pH = 3. Units are mandatory. A correct number without units loses the unit mark.
The answer is Acidic; pH = 3. NCERT Class 7 asks: turmeric + soap turns red because soap is basic.
Why This Works
PYQ patterns in acids, bases and salts (Class 7) repeat because the NCERT syllabus is fixed and examiners pick from a limited pool of testable concepts. Once you have solved 30-40 PYQs, you will recognise the question before you finish reading it.
NCERT Class 7 asks: turmeric + soap turns red because soap is basic.
Alternative Method
Some PYQs can be solved by elimination — rule out the obviously wrong MCQ options first, then pick the best remaining choice. This is a lifesaver when you are stuck on a concept but can eliminate two bad options using general biology sense.
Common Mistake
Students read the PYQ solution, nod “yes makes sense”, and move on without re-solving it themselves three days later. Passive reading does not build recall. Re-solve every PYQ from scratch at least twice before the exam.
Keep a PYQ logbook. For each question, note the date solved, whether you got it right, and the concept tested. Review the “got wrong” column every weekend.