Question

Property of the alkaline earth metals that increases with their atomic number is:
A. Ionisation energy
B. Solubility of their hydroxides
C. Solubility of their sulphates
D. Electronegativity

Answer 1

Hint: In the periodic table, the position of alkaline earth metals is in the 2^nd group. Their outermost shell configuration is ns² . Some examples are beryllium, magnesium, etc. The trend of atomic size on moving down the group is an increase in atomic size.

Complete Step by Step Answer:
Let's discuss all the options one by one.

Ionisation energy defines the energy needed in the removal of the valence electrons from the atom. We know, down the group, the electrons are added to the new shells. And this causes the weak interactive force of the nucleus and the valence electrons. Thus, a decrease of ionisation energy occurs with an increase in atomic number. Therefore, option A is wrong.

 From the above explanation, we find that there is a decrease in ionisation energy on moving down a group. So, their hydroxides are more soluble. Therefore, option B is right.

There is a decrease of the solubility of sulphate of the elements of the 2^nd group because of the domination of lattice energy over hydration energy. Thus, option C is wrong.

As the increase of atomic number occurs, the increase of shielding effect and decrease of effective nuclear charge occurs. Therefore, the capability to attract the electrons also decreases. Thus, option C is also wrong.

Hence, option B is right.

Note: There are two numbers of valence electrons in alkaline earth metals. To achieve stability, they readily lose these two electrons. Therefore, their nature is electropositive and they possess a low value of electronegativity.