When a hydrogen atom transitions from $n=2$ to $n=1$, it emits a photon. The recoil speed of the atom is $\frac{x}{5} \,m/s$. Find the value of $x$. (Use: mass of hydrogen atom $= 1.6 \times 10^{-27} \,kg$)

Energy of an electron (in $eV$) in the $2^{nd}$ orbit of a $He^{+}$ ion is (in $.6$)?

If the binding energy of the electron in a hydrogen atom is $13.6 \ eV$,the energy required to remove the electron from the first excited state of $Li^{++}$ is.....$eV$.

Energy of an electron in $n^{th}$ orbit of hydrogen atom is $\left( {k = \frac{1}{{4\pi {\varepsilon _0}}}} \right)$

In a hydrogen atom,when an electron jumps from the ground state to an excited state,the electron's ...

$A$ stationary hydrogen atom has an electron that transitions from the fifth energy level to the ground level. The velocity that the atom acquires as a result of photon emission will be: ($m$ is the mass of the atom,$R$ is Rydberg constant,and $h$ is Planck's constant).