Answer:

Introduction: In this question, we are given an octahedral crystalline variety of sulphur containing "X" S - S bonds in which the covalency of sulphur is "y". We are also given that this variety contains "Z" lone pairs of electrons. We need to find the value of (z-x-y).

Explanation:

Octahedral Variety of Sulphur: Octahedral variety of sulphur is a crystalline form of sulphur. It is a yellow, brittle and non-conducting solid. This variety of sulphur has an octahedral shape, which means that it has six sulfur atoms arranged in an octahedral shape.

X S - S Bonds: The given octahedral variety of sulphur contains "X" S-S bonds. Each sulfur atom is bonded to two other sulfur atoms in the octahedral arrangement. Therefore, the total number of S-S bonds in this variety of sulphur is 3X.

Covalency of Sulphur: The covalency of sulfur is the number of electrons that sulfur can share with other atoms to form covalent bonds. In the given octahedral variety of sulphur, the covalency of sulfur is "y". Therefore, each sulfur atom in this variety shares "y" electrons with two other sulfur atoms.

Lone Pairs of Electrons: The given octahedral variety of sulphur contains "Z" lone pairs of electrons. A lone pair of electrons is an electron pair that is not involved in bonding. In this variety of sulphur, each sulfur atom has one lone pair of electrons.

Calculation: We need to find the value of (z-x-y).

The total number of electrons contributed by sulfur atoms to form S-S bonds is 6y.

The total number of electrons contributed by sulfur atoms in the form of lone pairs is 2Z.

Therefore, the total number of electrons contributed by sulfur atoms is 6y+2Z.

The total number of electrons required to form S-S bonds in this variety of sulfur is 3X.

Therefore, the total number of electrons that are not involved in the formation of S-S bonds is (6y+2Z) - 3X.

Hence, we can write (z-x-y) as (2Z - 3X - 6y).

Conclusion: In this question, we have determined the value of (z-x-y) for an octahedral crystalline variety of sulfur. The value is given as (2Z - 3X - 6y).