when an electron collide with a photon it absorbs energy hv.then why anelectron can't absorb an energy 2hv by simultaneously colliding with twophotons.plz solve my prblm.

An electron cannot exist at two points at the same time.  So probability of simulataneous collision of an electron with two photons is negligible.

an electron cannot simulataneouls collide with two photons at a time,

its against the postulates of photoelectric effect!!

remember!!