The answer is: 25 grams.
Half-life is the time required for a quantity (in this example number of radioactive nuclei of carbon-14) to reduce to half its initial value.
Initial mass of sample: 100 grams.
After first half-life: 50% · 1000 g ÷ 100% = 50 g.
After second half-life: 0.5 · 50 g = 25 g.
Living things have carbon-14 in their organism, but when they died, the amount of C-14 they contain begins to decrease as the C-14 undergoes radioactive decay.
Measuring the amount of C-14 in a sample from a dead plant or animal when the animal or plant died.
