Question

An atom with atomic number 20 is most likely to combine chemically with the atom whose atomic number is
1) 3
2) 11
3) 17
4) 18

Answer 1

11...........is your answer

Answer 2

Answer : The correct answer is (3).

Explanation :

Given Atomic number is 20 which is calcium.

The electronic configuration of calcium is $1s^22s^22p^63s^23p^64s^2$

The electronic configuration of atomic number 17 is $1s^22s^22p^63s^23p^5$

This element forms anion. So, it will easily combine with element having atomic number 20 which is calcium.

For atomic number 3 and 11, the electronic configuration follows:

Atomic number 3: $1s^22s^1$

Atomic number 11: $1s^22s^22p^63s^1$

These two elements will loose 1 electron each to form stable ion. Hence, forming cations. These two elements would not combine with element having atomic number 20 because there will be cation-cation repulsion.

For atomic number 18, the electronic configuration is $1s^22s^22p^63s^23p^6$. This element is a stable element. Hence, will not combine with any of the elements.

Therefore, from all the atomic numbers, only element having atomic number 17 will combine with the element having atomic number 20.