the answer would be B an atom that has lost an electron
Answer : The energy of the photon emitted is, -12.1 eV
Explanation :
First we have to calculate the
orbit of hydrogen atom.
Formula used :

where,
= energy of
orbit
n = number of orbit
Z = atomic number of hydrogen atom = 1
Energy of n = 1 in an hydrogen atom:

Energy of n = 2 in an hydrogen atom:

Energy change transition from n = 1 to n = 3 occurs.
Let energy change be E.

The negative sign indicates that energy of the photon emitted.
Thus, the energy of the photon emitted is, -12.1 eV
"A neutron turns into a proton and an electron
Nominal mass does not change
atomic number decreases by one" -redbeardthegiant
This is the definition of a DNA mutation.
Depending on which part of the genome is affected, the consequences of a mutation may vary. A mutation is said to be hereditary if the mutated genetic sequence is transmitted to the next generation (see germinal mutations). It is one of the elements of biodiversity and one of the many factors that may be involved in the evolution of the species.