Answer
(i) 3
(ii) 3
(iii) 2
(iv) 1
(v) Infinite
(vi) 4
(vii) Infinite
Work Step by Step
(i) 1.25 g has three significant digits: all nonzero digits are significant.
(ii) 0.00125 g has three significant digits. Leading zeros are never significant.
(iii) 0.020 g has two significant digits: the 2 and the 0. Trailing zeros are significant when there is a written decimal point. (The 0 is explicitly given to indicate higher precision than a measurement of 0.02 g)
(iv) 100 g has one significant digit. Trailing zeros are not significant when there is no written decimal point.
(v) 100 cm/m has infinite significant digits. Because there are exactly 100 centimeters in 1 meter by definition, there is no need to worry about precision.
(vi) 4280. m has four significant digits. Trailing zeros are significant when there is a written decimal point. (The decimal point is given explicitly to show that the measurement was more precise than 4280 m, without a decimal).
(vii) $\pi$ effectively has an infinite number of digits.
