Significant Figures

Significant figures convey the precision of a measured value, and a clear set of rules decides which digits count. Leading zeros that merely fix the position of the decimal point are never significant, so the three zeros in 0.00 before the 4 are placeholders and contribute nothing. The non-zero digits 4 and 8 are always significant, and the zero sandwiched between them is also significant because trapped zeros count. Crucially, trailing zeros that appear after a decimal point are significant, since a careful experimenter writes them only to indicate measured precision. Therefore the digits 4, 0, 8, 0, 0, 0 are all significant, giving a total of six. The choice 3 wrongly ignores the meaningful trailing zeros, while 5 drops exactly one of them. The choice 8 incorrectly counts the leading placeholder zeros as well. This matches the NCERT rules for significant figures used throughout measurement chapters. A plausibility check helps: rewriting the value in scientific notation as 4.08000 × 10^-3 displays exactly six significant digits, confirming the answer.