Question

Match the atomic number 19, 15, 8, 4 and 2 with each of the following:
A. 19: A metal of valency one.
B. 15: A solid non-metal of period 3.
C. 8: A rare gas.
D. 2: A gaseous element with valency 2.
E. 4: An element of group 2.

Answer 1

To solve this we must know the elements having the given atomic numbers. From the atomic number of the elements we can determine the elements and thus, their given properties can be verified.

Complete answer:
We are given five atomic numbers 19, 15, 8, 4 and 2.
A. The element having atomic number 19 is potassium. The chemical symbol for potassium is ${\text{K}}$.
Potassium is an alkali metal and it belongs to group 1 of periodic table. Thus, the valency of potassium is one. Thus, potassium is a metal of valency one.
Thus, the option (A) 19: A metal of valency one is correct.
B. The element having atomic number 15 is phosphorous. The chemical symbol for phosphorus is ${\text{P}}$.
Potassium is solid in nature. It is non-metal and belongs to period 3 of the periodic table.
Thus, the option (B) 15: A solid non-metal of period 3 is correct.
C. The element having atomic number 8 is oxygen. The chemical symbol for oxygen is ${\text{O}}$.
Oxygen belongs to group 16 of the periodic table. Rare gases belong to group 18 of the periodic table. Thus, oxygen is not a rare gas.
Thus, the option (C) 8: A rare gas is not correct.
D. The element having atomic number 2 is helium. The chemical symbol for helium is ${\text{He}}$.
Helium belongs to group 18 of the periodic table. It is a rare gas.
All the rare gases have valency zero because they do not exchange or share electrons to form bonds. Thus, the valency of helium is zero.
Thus, the option (D) 2: A gaseous element with valency 2 is not correct.
E. The element having atomic number 4 is beryllium. The chemical symbol for beryllium is ${\text{Be}}$.
Beryllium is an alkaline earth metal. Beryllium belongs to group 2 of the periodic table.
Thus, the option (E) 4: An element of group 2 is correct.

**Thus, the correct options are (A), (B) and (E).

Note:**
We know that the atomic number is defined as the number protons in the nucleus of an atom. To solve this question we must correctly know all the atomic numbers along with their elements.