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): 12Number of electrons: 12Electron 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 = 52Number of electrons: 52Aufbau's rule and short notation: [Kr] 5s² 4d¹⁰ 5p⁴Hund's rule:  [Kr] 5s² 4d¹⁰ 5px↑↓ 5py↑ 5pz↑This configuration shows two unpaired elecctrons (same spin).

Hf (hafnium)

Z = 72Number of electrons: 72Aufbau's rule and short notation: [Xe] 4f¹⁴ 5d²6s²This configuration shows that there are not unpaired electrons (the las orbital 6s is complete with 2 electrons)

Si (silicon)

Z = 14Number of electrons: 14Aufbau's rule and short notation: [Ne] 3s² 3p²Hund'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.