Question

average velocity of a helium atom at 300 k is 2.40 *10^2 metre per second. what is wavelength (he =4)

Answer 1

Average velocity of a helium atom is 2.4 × 10² m/s = 240 m/s
Mass of one helium atom ,m = 4/6.023 × 10²³ g
= 4 × 1.66 × 10⁻²⁷ kg = 6.64 × 10⁻²⁷ kg

Now, use De - broglie wavelength
λ = h/mv
here h is plank's constant
λ = 6.6 × 10⁻³⁴/(6.64 × 10⁻²⁷ × 240)
= 0.004141 × 10⁻⁷ m
= 4.141 × 10⁻¹⁰ m

Answer 2

Ans is 0.416 nm

explained in notebook u can refer that......

Hope this helps you