If CI-35 has 18 neutrons, how many neutrons are
in CI-33?
(A) 17
(B) 16
(C) 15
(D) 18
(E) 19

B. 16

Explanation:

Cl -35 and Cl-33 have the same number of protons because it is the same element Cl.

Their masses are different because they have different number of neutrons.

Cl- 33 has 2 neutrons less than Cl-35.

35 - 33 = 2

If Cl-35 has 18 neutrons, then Cl-33 has 18-2=16 neutrons.

the answer is na (sodium)