When electrons are added to the outermost shell of a carbon atom, it forms
an anion that has a larger radius.
an anion that has a smaller radius.
a cation that has a larger radius.
a cation that has a smaller radius.

an anion that has a larger radius.

Explanation:

When a neutral atom gains electrons it forms an anion, and when it loses electrons it forms a cation. The radius or size of an anion is greater than a neutral atom. The radius or size of an cation is smaller than a neutral atom.

When electrons are added to the outermost shell of a carbon atom, it forms an anion that has a larger radius.

percent abundance for cu-63 can be shown as:

63 x + 65 (1-x) = 62.9296

65 - 62.9296 = 2 x

x = 1.035

thus, percent abundance for cu-63 is 1.035

percent abundance for cu-65 can be shown as:

63 x + 65 (1-x) = 64.9278

65 - 64.9278 = 2 x

x = 0.0361

thus, percent abundance for cu-63 is 0.0361

the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally