The work functions for metals A, B and C are respectively 1.92 eV, 2.0 eV and 5 eV. According to Einsteins equation, the metals which will emit photoelectrons for a radiation of wavelength 4100 Å is/are

(a) None

(b) A only

(c) A and B only

(d) All three metals

(a)

100 g will become 25 g in two half lives so it is 3200 years.

So, only metals having work function less than 3eV can emit photoelectrons for the incident radiation of wavelength 4100 Å.

we know that E=hc/lambda

now from given data 1eV=1-6*10^-19 J.

now find E value(which will be 3eV) and those having (A,B,C) energy greater than E will show.

Answer is (c) A and B only.