Question

Give the number of core electrons for Se.

A) 26               B) 30               C) 28               D) 32               E) 34

(1) Which the following orbitals can hold two electrons?

A) 3s                                     B) 2p_x                                                         C) 4d_xy

D) all of the above                E) none of the above

Answer 1

Q.1: Core electrons in an atom are electrons that do not participate in bond formation. Hence

Core electrons = Total electrons - Valence electrons

In Se there are a total of 34 electrons out of which 6 valence electrons participate in bond formation.

Hence core electrons in Se = 34 - 6 = 28 (answer)

Hence option (C) is correct.

Q.2: An orbital can hold a maximum of 2 electrons. Since 3s, 2px and 4dxy are all orbitals, all of the above can hold 2 electrons. Hence option (D): all of the above is correct.