GATE Computer Science (CS) 2019 Solved Papers

${\mathit{S}}_1$ : The set ${\mathit{L}}_{\mathit{R}\mathit{E}}$ is known to be countably infinite since it corresponds with set of turing machines.
${\mathit{S}}_2:$ Since syntactically valid $\mathit{C}$ programs surely run on Turing machines, this set is also a subset of set of Turing machines, which is countable.
${\mathit{S}}_3:$ Set of all languages $=2^{\mathit{\Sigma }}$ which is known to be uncountable. ${\mathit{\Sigma }}^{*}$ countably infinite
$\Rightarrow 2^{\mathit{\Sigma }}$ is uncountable.
${\mathit{S}}_4:$ Set of all non-regular languages includes set ${\mathit{L}}_{\mathrm{NOT}\mathrm{RE}}$ which is uncountable infinite and hence is uncountable.
So, ${\mathit{S}}_3$ and ${\mathit{S}}_4$ are uncountable.
Hence, $\mathit{B}$ is the correct answer.