When nuclear fission a. it must be initiated by bombardment with neutrons. b. two nuclei combine to produce a heavier nucleus. c. it is a spontaneous reaction. d. the chain reaction that results cannot be controlled.

Nuclear fission is a process in which a heavy nucleus is broken down into lighter nuclei.

Within a nucleus, the subatomic particles are held together by very strong forces of attraction. Neutrons which have the mass of a proton but no nuclear charges, is used to initiate fission reactions.

For example: The fission of U-235 into Barium (Ba-144) and Krypton (Kr- 89) is initiated by bombardment with neutron

₉₂U²³⁵ + ₀n¹   ⇒    ₉₂U²³⁶            

₉₂U²³⁶  ⇒      ₅₆Ba¹⁴⁴ + ₃₆Kr⁸⁹ + 3₀n¹

Ans) A

Nuclear fission is a process in which a heavy nucleus is broken down into lighter nuclei.

Explanation:

the answer is na (sodium)