The atomic masses of helium and neon are 4.0 and 20.0 amu respectively. The value of the de-Broglie wavelength of helium gas at $$-$$73$$^\circ$$C is M times the de-Broglie wavelength of neon at 727$$^\circ$$C. The value of M is

The maximum number of electrons in an atom in which the last electron filled has the quantum numbers n = 3, l = 2 and m = $$ - $$ 1 is

The radius of the first Bohr orbit of a hydrogen atom is 0.53 $$\times {10^-8}$$ cm. The velocity of the electron in the first Bohr orbit is

The number of unpaired electrons in the uranium (₉₂U) atom is