the periods are the horizontal rows on the table. identify the period of each of the following elements. 20…

Explanation:

Step1: Recall the periodic table

The periodic table arranges elements in periods (rows) and groups (columns).

Step2: Identify period of P

Phosphorus (P) has atomic number 15 and is in period 3.

Step3: Identify period of Ag

Silver (Ag) has atomic number 47 and is in period 5.

Step4: Identify period of He

Helium (He) has atomic number 2 and is in period 1.

Step5: Identify period of B

Boron (B) has atomic number 5 and is in period 2.

Step6: Identify period of Ca

Calcium (Ca) has atomic number 20 and is in period 4.

Answer:

20. 3
21. 5
22. 1
23. 2
24. 4