Which digits are always considered significant in a number?

The choice that indicates non-zero digits are always considered significant is correct because significant figures are fundamentally based on certain rules of numerical representation in scientific contexts. Non-zero digits (1 through 9) are always counted as significant because they contribute to the precision of the measurement.

When dealing with significant figures, leading zeros—that precede the first non-zero digit—do not count as significant because they do not convey any meaningful information about the magnitude of the number. Similarly, only whole numbers do not encompass the entire range of significant figures as fractions or decimal numbers can also contain significant digits. The same is true for zero digits; they can be significant in certain scenarios (such as trailing zeros in a decimal number) but are not always considered significant when they are merely leading or in a whole number without context. Thus, recognizing non-zero digits as always significant provides clarity and precision in data reporting and interpretation.