Which element has 3 valence electrons in the 4d sublevel? a. v b. nb c. cu d. tl

The correct answer is Option B.

Explanation:

Valence electrons are defined as the electrons which are present in outermost shell of an atom. This is determined by the electronic configuration of an element.

For the given options:

Option A: Vanadium (V)

The atomic number of this atom is 23 and number of electrons that are present are 23. The electronic configuration of vanadium is:

This element does not have 3 electrons in 4d-subshell.

Option B: Niobium (Nb)

The atomic number of this atom is 41 and number of electrons that are present are 41. The electronic configuration of niobium is:

This element have 3 electrons in 4d-subshell.

Option C: Copper (Cu)

The atomic number of this atom is 29 and number of electrons that are present are 29. The electronic configuration of copper is:

This element does not have 3 electrons in 4d-subshell.

Option D: Thallium (Tl)

The atomic number of this atom is 81 and number of electrons that are present are 81. The electronic configuration of thallium is:

This element does not have 3 electrons in 4d-subshell.

Hence, the correct answer is Option B.