Chemistry · Some Basic Concepts Of Chemistry · NEET
Split zeros into three types. (1) Leading zeros (in front, like 0.005) never count - they only show where the decimal is, so 0.005 has 1 significant figure. (2) Sandwich zeros (between non-zero digits, like 2.005) always count - so 2.005 has 4 significant figures. (3) Trailing zeros (at the end, like 0.200) count ONLY if there is a decimal point - so 0.200 has 3 significant figures. This 3-type split fixes most mistakes.
Just '100' with no decimal point has only 1 significant figure, because trailing zeros with no decimal are not counted. But 100. (with a dot) has 3, and 100.0 has 4. This is confusing, so NCERT says write it in scientific notation: 1 x 10^2 means 1 sig fig, 1.0 x 10^2 means 2, and 1.00 x 10^2 means 3. Scientific notation removes all doubt.
The two zeros in front (0.00...) are leading zeros. They do not measure anything; they only push the decimal point to the correct place. So they do not count. Only the 5 and the 2 are real measured digits, giving 2 significant figures. Remember: front zeros are just 'decimal placeholders', never significant.
No, it is actually easier. In scientific notation like 4.01 x 10^2, EVERY digit before the power of 10 is significant. So 4.01 x 10^2 has 3 significant figures and 8.256 x 10^-3 has 4. The x 10^n part never affects the count. This is why NEET-level students prefer scientific notation - it makes counting simple.
Exact counted numbers (like 2 balls or 20 eggs) and defined constants have INFINITE significant figures. You can write 20 = 20.000000... forever. This matters in NEET calculations: when a number comes from counting or from a definition, it never limits your significant figures in a final answer.
NEET numerical questions in physical chemistry (density, molarity, atomic mass) expect answers with the correct number of significant figures. Writing too many or too few digits can make your answer not match the given option. Knowing these rules also helps you round off correctly in the next step, so you pick the exact option NTA wants.
The numbers 17.0145 and 21.0235 were rounded to three figures after the decimal point. The resulting numbers, respectively, are:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They are the meaningful digits in a measured number - the digits we are sure about plus one last digit that is a little uncertain. For example, in 11.2 mL, the 11 is certain and the 2 is the uncertain digit, giving 3 significant figures.
It has 4. All non-zero digits (2 and 5) count, and the two zeros between them are sandwich zeros that always count.
No. Zeros before the first non-zero digit (like the zeros in 0.0052) are never significant. They only fix the position of the decimal point. So 0.0052 has 2 significant figures.
Write it as 100. with a decimal point, or better, as 1.00 x 10^2 in scientific notation. Plain 100 has only 1 significant figure.
Infinite. Counted objects like 20 eggs and defined values have unlimited significant figures, so they never limit the precision of your final answer.
