The kinetic energy of an electron revolving around a nucleus will be

An electron in the hydrogen atom jumps from the first excited state to the ground state. What will be the percentage change in the speed of the electron (in $\%$)?

The magnetic field at the centre due to the motion of an electron in the first Bohr orbit is $B$. The magnetic field due to the motion of an electron in the second Bohr orbit at the centre will be

In Bohr's model,the atomic radius of the first orbit is $r_0$,then the radius of the third orbit is

Suppose in a hypothetical world,the angular momentum is quantized to be even integral multiples of $\frac{h}{2 \pi}$. According to Bohr's model,what will be the largest possible wavelength emitted by hydrogen atoms in the visible range in this world (in $text{ nm}$)? (Consider $hc = 1242 \text{ eV-nm}$)

The de-Broglie wavelength of the electron in the ground state of the hydrogen atom is $...... \text{ } \mathring{A}$ (radius of the first orbit of hydrogen atom $= 0.53 \text{ } \mathring{A}$).