In group 1 of the periodic table three elements X, Y and Z have atomic radii 133 pm, 95 pm and 65 pm respectively. Giving a reason, arrange them in the order of increasing atomic numbers in the group.

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Solution

Step-1: Introduction
Atomic radii is the distance of the electrons in the outermost shell from the atomic nucleus. It increases from top to bottom in a group and decreases from left to right in a period but is highest for a noble gas.
Step-2: Atomic radii of X, Y and Z
In group 1, the atomic radii increase due to increase in valence shell.
In a period, atomic size drops as move on from left to right. The reason is due to rise in proton number and it results in higher electrons attraction.
So, as atomic number rises atomic radii downs.
The increasing order of atomic number in the group is given as Z, Y and X.
Element Z Y X
Atomic radii (in pm) 65 95 133
X will have higher atomic number while Z has the lower atomic number.
Final answer
Therefore, the increasing order of atomic numbers in the group is Z, Y and X.

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