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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