Question

Helium belongs to a group of elements in which are largest in size in respective bond

Answer 1

so what's the question be specific

Answer 2

Francium.

The van der Waals radius (also known as the nonbonding atomic radius) is the radius of an atom that is not bound to other atoms. It is calculated by measuring the distance between atomic nuclei in a crystal lattice that are in direct but nonbonding contact with each other.

For metals, the covalent atomic radius (also known as the bonding atomic radius) is half the distance between two neighbouring atoms in a metallic crystal, or half the distance between similarly bound atoms for nonmetals.

Helium belongs to the group of noble gases. Atomic radii of different elements vary predictably in a periodic table. They decrease from left to right across the table and increase from top to bottom in a group.

Thus the last element in the group of Helium will have the largest size in respective bond radius. The last element in the group is Francium.