A bulb is emitted electromagnetic radiation of $$660 \mathrm{~nm}$$ wavelength. The total energy of radiation is $$3 \times 10^{-18} \mathrm{~J}$$. The number of emitted photon will be

$$\left(h=6.6 \times 10^{-34}\right) \mathrm{J} \times \mathrm{s}, c=3 \times 10^8 \mathrm{~m} / \mathrm{s}$$

Assertion : The chemical properties of different isotope are same.

Reason : Isotopes having same number of neutron.

The work function of a metal is $$4.2 \mathrm{~eV}$$. If radiation of 2000 $$\mathop A\limits^o$$ fall on the metal then the kinetic energy of the fastest photoelectron is