Question

1. using the characteristics of the electron - configuration of elements, which elements are described below in order from a to d? a. contains 7 electrons in its fourth energy level b. contains 3 unpaired electrons in its third energy level c. contains 2 electrons in its fifth energy level d. contains the first d electron

Explanation:

Step1: Analyze option A

Elements with 7 electrons in the fourth - energy level are in the halogen group in the fourth period (Br). Elements with 3 unpaired electrons in the third - energy level are in Group 15 in the third period (P). Elements with 2 electrons in the fifth - energy level are in Group 2 in the fifth period (Sr). Elements with the first d - electron are in the first transition - metal group in the fourth period (Sc).

Step2: Match with elements

For A: 7 electrons in fourth energy level is Br, 3 unpaired in third is P, 2 in fifth is Sr. For B: no clear match as described. For C: no clear match as described. For D: no clear match as described.

Answer:

Br, P, Sr, Sc