de - Broglic wavelength of electron in nth Bohr orbit is............
According to de Broglie hypothesis, the wavelength of an electron in the nth Bohr orbit is given by: $$ ext{wavelength} = rac{2 ext{π}r}{n} $$ Here, $r$ is the radius of the nth orbit and $n$ is the principal quantum number. This formula is derived from the quantization condition of angular momentum in Bohr's model of the atom, where $mvr = nrac{h}{2 ext{π}}$. Therefore, the correct option is: $$rac{2 ext{π}r}{n} A^ ext{∘}$$