Option D: Calcium (Ca)

The atomic number of bromine is 35 thus, the electronic configuration will be:

Br:[Ar]3d^{10}4s^{2}4p^{5}

Here, [Ar] defines electronic configuration of argon noble gas with stable electronic configuration and atomic number 18.

The energy level is defined by principal quantum number, n. Since, the valence electrons in bromine are in 4p thus, energy level will be 4 (principal quantum number).

Now, atomic number of barium is 56 and its electronic configuration is as follows:

Ba:[Xe]6s^{2}

Here, [Xe] defines electronic configuration of xenon noble gas with stable electronic configuration and atomic number 54. The valence electronic shell is 6s^{2} thus, number of valence electrons are 2.

A. Potassium (K): Atomic number is 19 thus, electronic configuration will be:

K:[Ar]4s^{1}

Here, [Ar] defines electronic configuration of argon noble gas with stable electronic configuration and atomic number 18.

Now, the energy level is same as that of Br but valence electron is 1 which is not equal to that of Ba.

Thus, this is incorrect option.

B. Beryllium (Be): Atomic number is 4 thus, electronic configuration will be:

Be:[He]2s^{2}

Here, [He] defines electronic configuration of helium noble gas with stable electronic configuration and atomic number 4.

Now, the number of valence electrons are same as that of Ba but the energy level is not same as that of Br.

Thus, this is incorrect option.

C. Cadmium (Cd): Atomic number is 48 thus, electronic configuration will be:

Cd:[Kr]4d^{10}5s^{2}

Here, [Kr] defines electronic configuration of krypton noble gas with stable electronic configuration and atomic number 36.

Now, the number of valence electrons are same as that of Ba but the energy level is not same as that of Br.

Thus, this is incorrect option.

D. Calcium (Ca): Atomic number is 20 thus, electronic configuration will be:

Ca:[Ar]4s^{2}

Here, [Ar] defines electronic configuration of argon noble gas with stable electronic configuration and atomic number 18.

Now, it has energy level same as that of Br and number of valence electron is also same as that of Ba thus, it is correct option.

Therefore, calcium (Ca) is the correct element.