Mark out the incorrect statement:
A) A free neutron can transform itself into a proton
B) A free proton can transform itself into a neutron
C) In beta minus decay, the electron originates from the nucleus
D) All of the above

Hint: In Beta minus decay, a neutron inside the nucleus converts into a proton and releases an antineutrino along with a high energy electron. The inverse of this process called inverse beta is also possible, but only inside the nucleus.

Complete answer:
Let us analyze all the options one by one.
Option A) states that a free neutron can transform itself into a proton. A free neutron is unstable and emits a proton from the nucleus. This decay happens because the mass of the neutron is slightly higher than the mass of the proton. This process is known as negative-Beta decay.
Hence, option A) incorrect statement.
Option B) states that a free proton can transform itself into a neutron. This is absolutely not possible since the mass of a proton is slightly lesser than the mass of the neutron. Since, according to the law of conservation of mass, mass can neither be created nor destroyed, a free proton without the influence of any other masses, cannot create a body of greater mass, that is the neutron. This process is however possible inside the nucleus and is known as inverse beta.
Hence, option B) is the correct statement.
Option C) states that In beta minus decay, the electron originates from the nucleus. This is true since in beta minus decay, a neutron inside the nucleus decays into a proton, an electron and an antineutrino. Therefore, this electron originates from the nucleus. Therefore this statement is correct.
Hence, the only incorrect statement is option A).

Therefore the required answer is option A).

Note:
Students must note that a beta decay process or negative beta decay is possible both inside and outside the nucleus. However, an inverse beta process where a proton converts into a positron, neutron and neutrino, is possible only inside the nucleus. This is because the proton is lesser in mass than a neutron and can only perform this process under the influence of binding forces and other bodies (that is protons and neutrons) inside the nucleus. However, a free proton does not have these influences and thus, cannot perform this process.