Which of the following ions has the smallest ionic radius?
a. c4+
b. b3+
c. be2+
d. li+

The ion is  which  has the smallest ionic radius is C4+.

The size of the atomic radius in the periodic table increases as we go down

the group while the atomic radius size decreases from left to right across the period. It is also pertinent to note that cation are usually smaller than its

parent atom.

The order of the elements from left to right across the period include Li+,

Be2+ , Be3+ , C4+

Therefore the atom with the biggest atomic radius is B3+ and the smallest is  

C4+.

The C4+ ion therefore has the smallest ionic radius

Li+ > Be2+ > Be3+ > C4+

Read more on link

The C4+ ion has the smallest ionic radius

Explanation:

In the periodic table, the size of an atom increases on going downwards in a group.

On the other hand, in a period, size decreases on going from left to right

The size of cation is smaller than its parent atom.

Lithium-ion (Li+) is the most left so it has the biggest radius.

More to the right ( this means a smaller ionic radius) , we have Berylium-ion (Be2+).

More to the right, so smaller than Be2+, we have B3+

The ion the most to the right, we have C4+

The C4+ ion has the smallest ionic radius

Li+ > Be2+ > Be3+ > C4+

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).