From photoelectric equation, E=φ0+ K.E. max For metals P and Q E1=φP+KEP ⇒E1−4=EP and E1−4.5=EO EP=2EO (given) ∴E1−4=2(E1−4.5) ⇒E1=5eV E1−4=EP⇒5−4=EP ∴EP=1eV and EQ=ER=0.5eV For metal R,E2−φR=KER ∴E2−5.5=0.5 ∴E2=0.5+5.5=6eV