Question

Atomic number of calcium is:

A. 18

B. 19

C. 20

D. 21

Answer 1

Hint: To give the correct atomic number of calcium, we should know the position of calcium in the periodic table. If we know about the group and period of calcium we can easily tell the atomic number of calcium.

Step by step answer:
To determine the correct atomic number of calcium we should first know about the group and period of calcium. It will help us in determining the correct atomic number of calcium. We should know that calcium is a chemical element with the symbol Ca. When we observe the periodic table, we will find that calcium is present in S block, group 2 and period 4 of periodic table. We should know that group 2 is known by the name of alkaline earth metals. So, from this we can say that the calcium atomic number is 20.
We should note that, in option A, 18 is the atomic number of noble gas argon.
In option B, 19 is the atomic number of potassium and is the member of alkali metal group.
Option C is our correct answer. Atomic number of calcium is 20.
In option D, scandium has the atomic number 21. It is a D block element.
We should note that, a calcium atom has twenty electrons, arranged in the electron configuration [Ar] \[4{{s}^{2}}\]. And like the other elements placed in group 2 of the periodic table. We should note that calcium has two valence electrons in the outermost s-orbital, which are very easily lost in chemical reactions to form a di-positive ion with the stable electron configuration of a noble gas, in this case argon. Hence, calcium is almost always divalent in its compounds, which are usually ionic.
So, the above discussion proves that calcium has atomic number 20, and option C is correct.

Note: For our knowledge let us know about some uses of calcium. We use metallic calcium in steel making. We should know that calcium has a strong chemical affinity for oxygen and sulphur. Its oxides and sulphides, once formed, give liquid lime aluminate and sulphide inclusions in steel which float out.
We should know that calcium is a common constituent of multivitamin dietary supplements.