During a nuclear reaction, an isotope of a certain atom gives off a particle consisting of two protons and two neutrons, and the atom becomes a different element. Which type of radioactive decay has occurred?

Type of radioactive decay which has occurred is an alpha decay.

Explanation:

Type of radioactive decays:

Alpha decay is defined as the decay process in which alpha particle is released. In this process, a heavier nuclei decays into a lighter nuclei. The alpha particle released carries a charge of +2 units and a mass of 4 units.Beta decay is defined as the process in which beta particle is emitted. In this process, a neutron gets converted to a proton and an electron. The released beta particle is also known as electron.Gamma decay In this process, an unstable nuclei releases excess energy by a spontaneous electromagnetic process and gamma -radiations are emitted. These radiations does not carry any charge and are electrically neutral.

Carbon monoxide is the answer: )