Option A is incorrect as it is a neutralization reaction. Option C is incorrect as it an oxidation reaction, the rusting of iron to form iron oxide.
Option B and D are nuclear reactions called alpha decay.
In an alpha decay, a helium atom is released, and the daughter nucleus formed has atomic number 2 less than the parent nucleus and mass number 4 less than the parent nucleus.
It is seen that in first and third ones elements are not changed but only their chemical arrangements are changed. both are chemical reactions.
In the second and last one elements are changed after the reaction and as we know non chemical reactions are not capable of doing that so they are nuclear reactions.
There are other ways to tell like checking number of neutrons as well but in this simple case I don't think it is necessary to check those.
