b
According to $Wein's$ displacement law
${\lambda _m}T = constant$ $...(i)$
For star $P,$ instensity of violet colour is maximum
For star $Q,$ instensity of red colour is maximum.
For star $R,$ intensity of green colour is maximum.
$Also,{\lambda _r} > {\lambda _g} > {\lambda _v}$
Using equation $(i)$, ${T_r} < {T_g} < {T_v}$
${T_Q} < {T_R} < {T_P}$