Here it is
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Nuclear reactions are temperature independent and uranium 235 undergoes a decay of 7 alpha particles to get converted into Pb
Specific activity depends on the activity per unit radioactive nuclei and whereas activity depends on number of atoms in the sample which are radioactive.

Option D seems like a correct one, i-e ?7 α− particles will be emitted when U235 decay to stable nuclei.?
Reason:
Option A can not be accurate as activity depends on the number of atoms in the sample, which are radioactive. As for the second option, Specific activity depends on the activity per unit of radioactive nuclei. The third option is neither valid as the temperature does not affect nuclear reactions. So option D is correct.
Explanation:
Uranium-235 decay into thorium-231 and an alpha particle. Uranium-235 and more extensive or massive nuclei become more stable by emitting alpha particles.
Alpha particle is a helium nucleus composed of two protons and two neutrons. This process is known as alpha decay.