How does gamma decay differ from both alpha decay and beta decay?
no change in mass number occurs.
a nucleus becomes more stable.
no new element forms.
a nucleus releases protons and neutrons.

No new element forms.

Gamma decay differs from alpha decay and beta decay since there is no new element forms.

Explanation:

Among the three types of radio-active decay namely alpha decay, beta decay and gamma decay , gamma decay is the only one where a change in mass number or atomic number doesn’t occur. In gamma decay electromagnetic radiations are produced and the decaying atom doesn’t undergo changes   in atomic number or mass number. Thus no new elements are formed.

In alpha decay He nuclei is produced and the atomic number of decaying atom reduces by 2 and its mass number reduces by 4. In beta decay electrons  or positrons are produced and depending on whether the product is electron or positron the atomic number of the atom increases or decreases by 1 respectively.