Chemistry · Some Basic Concepts Of Chemistry · NEET
No. Zeros that come before the first non-zero digit are NEVER significant. They only tell you where the decimal point sits. So 0.0052 has only 2 significant figures (the 5 and the 2). The zeros in front are just placeholders. Same for 0.03 - it has only 1 significant figure. Remember: leading zeros never count.
3 significant figures. Work left to right: the first three zeros are leading zeros (before the first non-zero digit 5), so they do NOT count. The 5 counts. The two zeros AFTER the 5 come after the decimal point, so they DO count. So you count 5, 0, 0 = three significant figures. This is a favourite NEET trap because the leading zeros and trailing zeros are treated in opposite ways.
Yes, always. A zero trapped between non-zero digits is called a 'sandwich zero' and it is always significant, decimal point or not. So 2.005 has 4 significant figures (2, 0, 0, 5). Also 40506 has 5 significant figures. These zeros can never be removed, so they must be counted.
By NCERT rule, 100 (with no decimal point) has only 1 significant figure. The two trailing zeros are NOT significant because there is no decimal point to lock them in. But 100. (with a dot) has 3, and 100.0 has 4. This is confusing, so NEET writers prefer scientific notation: 1x10^2 means 1 sig fig, 1.0x10^2 means 2, and 1.00x10^2 means 3.
A trailing zero after a decimal point (like the last 0 in 0.200) is written on purpose to show the measurement was that precise, so it is meaningful. But in a whole number like 4500, the zeros might just be placeholders (was it exactly 4500 or rounded?). Without a decimal point we cannot be sure, so NCERT treats those trailing zeros as NOT significant. The decimal point removes the doubt.
Ignore the power of 10 completely. Only count the digits in front (the coefficient). So 4.01x10^2 has 3 significant figures and 8.256x10^-3 has 4. This is why scientific notation is so useful - every digit you write is significant, so there is no confusion about zeros.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
3. The leading zero (before the decimal digit) does not count, but the 2 and both trailing zeros after the decimal point count. So 2, 0, 0 = 3 significant figures.
Only 1, because there is no decimal point, so the trailing zeros are not significant. To show more precision, write 2.00x10^2 (3 sig figs) or 200. with a decimal point (3 sig figs).
Yes. Zeros sitting between two non-zero digits are always significant, whether or not there is a decimal point. For example 5007 has 4 and 30.09 has 4 significant figures.
Yes. 100 has 1 significant figure (no decimal, trailing zeros do not count), while 100.0 has 4 significant figures because the decimal point makes all the trailing zeros count.
NEET Chemistry numerical questions on mole concept, concentration and calculations expect your final answer rounded to the correct number of significant figures. Miscounting zeros gives a wrong-looking answer and loses marks, so this rule is a quiet but frequent trap.
