Question

Alkali metals in each period have?
A.Smallest size
B.Lowest ionisation energy
C.Highest ionisation energy
D.Highest electronegativity

Answer 1

So, the alkali metals are the metals or all elements of the group $1$ of the periodic table. Since, the group $1$ lies in the s-block elements, so the alkali earth metals are the s- block elements of the periodic table. They are very soft metals.

Complete answer:
so, as we knew that, the alkali metals are the group $1$ elements or the s-block elements. So they consist of the elements like - Lithium (Li), Sodium (Na), Potassium (K), rubidium (Rib), Caesium (Cs), and Francium (Fr).
These all are soft metals. So let’s have a look at their common properties for better understanding of the group $1$ elements.
Since, there are the group $1$ elements and as we know when we move from left to right in the periodic table , then the size of the elements decreases, hence , we can say for sure, these elements have the largest size.
And as also we know that the ‘ionisation energy ‘ is the energy required to remove the most loosely bound electron from its valence shell from the neutral gaseous atom or the molecule. So since, we know that alkali metals having the largest size, have electrons more loosely bound, so they need less energy to remove the electrons from the outermost shell and so they have low ionisation energy.
Hence, from the above discussion we can say that the Alkali metals in each period have the lowest ionisation energy.

Therefore option B is the correct answer.

Note:
When we talk about the electronegativity of the alkali metals, being the largest in size in each period, they remove electrons easily and hence, they are the most electropositive elements in their periods.