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According to Bohr's model, the highest kinetic energy is associated with the electron in the
For any one-electron (hydrogen-like) species, Bohr’s model gives the total energy in the $$n^{\text{th}}$$ orbit as
$$E_n = -\frac{13.6\,\text{eV}\;Z^{2}}{n^{2}}$$
where $$Z$$ is the atomic (nuclear) charge.
The kinetic energy in that orbit is related to the total energy by
$$KE_n = -E_n$$
(because in Bohr’s model $$E_n = KE_n + PE_n$$ with $$PE_n = -2\,KE_n$$).
Hence
$$KE_n = \frac{13.6\,\text{eV}\;Z^{2}}{n^{2}} \quad -(1)$$
so $$KE_n$$ is directly proportional to $$\dfrac{Z^{2}}{n^{2}}$$.
Now evaluate $$\dfrac{Z^{2}}{n^{2}}$$ for each option:
Option A: $$H$$ atom ($$Z = 1,\; n = 1$$)
$$\dfrac{Z^{2}}{n^{2}} = \dfrac{1^{2}}{1^{2}} = 1$$
Option B: $$He^{+}$$ ($$Z = 2,\; n = 1$$)
$$\dfrac{Z^{2}}{n^{2}} = \dfrac{2^{2}}{1^{2}} = 4$$
Option C: $$He^{+}$$ ($$Z = 2,\; n = 2$$)
$$\dfrac{Z^{2}}{n^{2}} = \dfrac{2^{2}}{2^{2}} = 1$$
Option D: $$Li^{2+}$$ ($$Z = 3,\; n = 2$$)
$$\dfrac{Z^{2}}{n^{2}} = \dfrac{3^{2}}{2^{2}} = \dfrac{9}{4} = 2.25$$
The largest value is $$4$$ for Option B, meaning the electron in the first orbit of $$He^{+}$$ possesses the highest kinetic energy.
Therefore, the correct choice is:
Option B which is: First orbit of $$He^{+}$$
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