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We determine the number of significant figures with the help of the following rules:

• All non-zero digits are significant.
• Zeros present in between non-zero digits are significant.
• Zeros which come after the decimal point are significant(trailing zeros).
• Zeros which come before the decimal and any non-zero number are insignificant (leading zeros) since they are only used to depict the place of the decimal.
• Exact numbers have an infinite number of significant digits.

a) 0.0055 g active ingredients: The three zeroes are leading and hence insignificant, thus total number of significant figures = 2

b) 12 tablets: The number of significant figures in exact numbers is always infinite.

c) 3% hydrogen peroxide: The number of significant figures is 1.

d) 5.5 ounces: The number of significant figures is 2, since both digits are non-zero.

e) 473 mL: The number of significant figures is 3.

f) 1.75% bismuth: The number of significant figures is 3, they are non-zero digits.

g) 0.001% phosphoric acid: The number of significant figures is 1, since the zeroes are leading zeros.

h) 99.80% inert ingredients: The number of significant figures is 3, since we have a trailing zero which is significant.