$(24).$ Which radical$($s$)$ is the least stable?

R

s

T

$($a$)f$

$($b$)s$

$($c$)T$

$($d$)R$ and $S$ are approx the same

$(25)$ A reaction where $2$ reactants exchange parts to give $2$ new products.

$($a$)$ substitution

$($b$)$ nucleophile

$($c$)$ heteroly tic bond breakage

$($d$)$ radical reaction

$(26)$ wnich graph of potential energy VS $C_1-c_2$ bond rotatim $(0-360$ degrees$)$ is the best representation of chloroethane?