Asample of a radioactive nuclide has a mass of 10 g. how many half lives must transpire until less than 21% of the original sample is present?

3 half-lives.

Explanation:

Half-life time is constant for first-order reaction.

21% of the sample (10 g) represents (10.0 x 0.21 = 2.1 g).

10 g (first half-life) → 5 g (second half-life) → 2.5 g (third half-life) → 1.25 g.

∴ 3 half-lives are needed for the sample to reach less than 21% (<2.1 g) of its initial value.

the correct answer would be d. hope this !

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.