A particle is moving with 3 times faster than speed of electron. Ratio of wavelength of particle and electron is 1.8*10^-4, then the particle is:- a) Neutronb) Alpha particlec) Deutrond) Tritium

We use the de Broglie expression:

λ=hmv

So we can write:

λe=hmeve (1)

λp=hmpvp (2)

vp=3ve (3)

Substituting (3) into (2)⇒

λp=hmp3ve (4)

Dividing (4) by (3)⇒

λpλe=hmp3ve.meveh=1.8×10−4

∴me3mp=1.8×10−4

memp=5.4×10−4

This ratio is 5.39522×10−4 for a neutron and 5.36099×104 for a proton, so a neutron seems to be the most likely candidate for the particle in question, though I guess there could be others.