Which of the following measurements is expressed to three significant figures?
a) 0.007 m
b)7077 mg
c)7.30 x 10^-7
d) 0.070 mm

Explanation :

Significant figures : The figures in a number which express the value -the magnitude of a quantity to a specific degree of accuracy is known as significant digits.

Rules for significant figures:

Digits from 1 to 9 are always significant and have infinite number of significant figures.

All non-zero numbers are always significant. For example: 654, 6.54 and 65.4 all have three significant figures.

All zero’s between integers are always significant. For example: 5005, 5.005 and 50.05 all have four significant figures.

All zero’s preceding the first integers are never significant. For example: 0.0078 has two significant figures.

All zero’s after the decimal point are always significant. For example: 4.500  have four significant figures.

All zeroes used solely for spacing the decimal point are not significant. For example : 8000 has one significant figure.

1. 0.007 has one significant figure.

2. 7077 has four significant figures.

3.  has three significant figures.

4. 0.070 has two significant figures.

fe 55.85 g/mol and h2o 18.02 g/mol.

i think it's letter a.