Answer: The correct option is 4.
Explanation: All the options will undergo some type of radioactive decay processes. There are 3 decay processes:
1) Alpha decay: It is a decay process in which alpha particle is released which has has a mass number of 4 and a charge of +2.
\(_Z^A\textrm{X}\rightarrow _{Z-2}^{A-4}\textrm{Y}+_2^4\alpha\)
2) Beta-minus decay: It is a decay in which a beta particle is released. The beta particle released has a mass number of 0 and a charge of (-1).
\(_Z^A\textrm{X}\rightarrow _{Z+1}^A\textrm{Y}+_{-1}^0\beta\)
3) Beta-plus decay: It is a decay process in which a positron is released. The positron released has a mass number of 0 and has a charge of +1.
\(_Z^A\textrm{X}\rightarrow _{Z-1}^A\textrm{Y}+_{+1}^0\beta\)
For the given options:
Option 1: This nuclei will undergo beta-plus decay process to form \(_{25}^{53}\textrm{Mn}\)
\(_{26}^{53}\textrm{Fe}\rightarrow _{25}^{53}\textrm{Mn}+_{+1}^0\beta\)
Option 2: This nuclei will undergo beta-minus decay process to form \(_{80}^{198}\textrm{Hg}\)
\(_{79}^{198}\textrm{Au}\rightarrow _{80}^{198}\textrm{Hg}+_{-1}^0\beta\)
Option 3: This nuclei will undergo a beta minus decay process to form \(_{56}^{137}\textrm{Ba}\)
\(_{55}^{137}\textrm{Cs}\rightarrow _{56}^{137}\textrm{Ba}+_{-1}^0\beta\)
Option 4: This nuclei will undergo an alpha decay process to form \(_{85}^{216}\textrm{At}\)
\(_{87}^{220}\textrm{Fr}\rightarrow _{85}^{216}\textrm{At}+_2^4\alpha\)
Hence, the correct option is 4.