Consider the case of a radioactive element X which decays by

Consider the case of a radioactive element X which decays by electron (beta) emission with a half-life of 4 days to a stable nuclide of element Z. Which of the following statements is CORRECT?
(a) After 8 days the sample will consist of one-fourth element Z and three-fourths element X.
(b) Element Z will weigh exactly the same as element X when decay is complete (weighed to an infinite number of significant figures).