Represent the change in the nucleus of a radioactive element

1. Represent the change in the nucleus of a radioactive element when a β particle is emitted.
2. What is the name given to elements with same mass number and different atomic number?
3. Under which conditions does the nucleus of an atom tend to be radioactive?

Answer

i.

ii.

iii. When
    -neutron proton ratio becomes more than 1.3 to 1.5
    -nucleus has more/excess mass.
    -nucleus has excess energy.