A radioactive sample starts at 256 g. How much undecayed material remains after 4 half-lives?

A) 16 g

B) 24 g

C) 32 g

D) 8 g

Answer: A

Explanation: Use remaining mass = initial mass ÷ 2^(number of half-lives) for the stated idealized conditions. Substitution gives 256 ÷ 2^4 = 16 g.