Which of the following decays result in a decrease in the atomic...

In $\alpha$-decay, the nucleus emits an $\alpha$-particle (^{4}_{2}\text{He}$). The atomic number$Z$decreases by$2$.<br><br>In$\beta^{+}$-decay, a proton is converted into a neutron with the emission of a positron (^{0}_{+1}\text{e}$). The atomic number $Z$ decreases by $1$.

In $\beta^{-}$-decay, a neutron is converted into a proton with the emission of an electron (^{0}_{-1}\text{e}$). The atomic number$Z$increases by$1$.<br><br>In$\gamma$-decay, only the energy state of the nucleus changes. The atomic number$Z$remains unchanged.<br><br>Thus,$\alpha$-decay and$\beta^{+}-decay result in a decrease in the atomic number.