How many of the following elements have 2 unpaired electrons in the ground state? C Te Hf Si

A) 1.

B) 2.

C) 3.

D) 4.

Option C) 3.

C, Te, and Si have two unpaired electrons in the ground state.

Explanation:

You must draw the electron configuration.

C (carbon)

Atomic number (Z) : 12 Number of electrons: 12 Electron configuration of ground state, following Aufbau rules (filling orbitals in order of increasing energy):

1s² 2s² 2p²

Electron pairing following Hund's rules (fill different orbitals of same energy, with same spin, before adding a second electron, with opposite spin, to an orgital).

1s² 2s² 2px↑ 2py↑

As you see, these configuration shows two unpaired electrons (same spin) in the ground state.

Te (tellurium)

Z = 52 Number of electrons: 52 Aufbau's rule and short notation: [Kr] 5s² 4d¹⁰ 5p⁴ Hund's rule: [Kr] 5s² 4d¹⁰ 5px↑↓ 5py↑ 5pz↑ This configuration shows two unpaired elecctrons (same spin).

Hf (hafnium)

Z = 72 Number of electrons: 72 Aufbau's rule and short notation: [Xe] 4f¹⁴ 5d²6s² This configuration shows that there are not unpaired electrons (the las orbital 6s is complete with 2 electrons)

Si (silicon)

Z = 14 Number of electrons: 14 Aufbau's rule and short notation: [Ne] 3s² 3p² Hund's rule: [Ne] 3s² 3px↑ 3py↑ This configuration shows two unpaired electrons.

Conclusion: C, Te and Si, have two unpaired electrons (same spin) in the ground state.