Regents Chemistry Exam June 2024 Question 32
32 The mass of a sample of nickel is determined to be 20.40 grams. How many significant figures are used to express this mass?
(1) 1 (3) 3
(2) 2 (4) 4
Solution:
Here are the rules for counting significant figures. All non-zero digits are significant. This means all numbers: 1,2,3,4,5,6,7,8, and 9 are significant. For example 3.6 has two significant figures.
All zeroes in between non-zero numbers are significant. For example, 503 has three significant figures, including the zero in-between two numbers.
Leading zeroes (zeroes to the left of a number) are not significant. For example: 0.00056 has only two significant figures (5 and 6).
Trailing zeros to the right of a decimal point are significant. For example zeroes in 8.400 are significant.
Terminal zeros in a number without an explicit decimal point may or may not be significant (for example 300). To remove the confusion, we should write out these number using scientific notation.
The correct answer is 4 significant figures, Choice 4.
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