(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.