The number of valence electron and the valency with respect to hydrogen are equal for:

• (A) Sulphur
• (B) Silicon
• (C) Phosphorus
• (D) Chlorine

To determine which element has an equal number of valence electrons and valency with respect to hydrogen, let's first clarify what we mean by valence electrons and valency. Valence electrons are the electrons in the outermost shell of an atom, while valency refers to the ability of an atom to bond with other atoms, often determined by the number of electrons it can gain, lose, or share to achieve a full outer shell.

Analyzing Each Element

Now, let's look at each of the options provided:

• Sulphur (S): Sulphur has 6 valence electrons. Its common valency is 2 (it can gain or share 2 electrons to achieve a stable configuration). Therefore, the number of valence electrons and valency are not equal.
• Silicon (Si): Silicon has 4 valence electrons. Its typical valency is also 4, as it can share these electrons to form covalent bonds. Here, the valence electrons and valency are equal.
• Phosphorus (P): Phosphorus has 5 valence electrons. Its common valency is 3 or 5, depending on the compounds it forms. Thus, the valence electrons and valency do not match.
• Chlorine (Cl): Chlorine has 7 valence electrons and a valency of 1, as it typically gains one electron to achieve a full outer shell. Again, these numbers are not equal.

Conclusion

From this analysis, we can see that the only element where the number of valence electrons equals its valency with respect to hydrogen is Silicon (Si). It has 4 valence electrons and a valency of 4, allowing it to form stable bonds effectively.

This relationship is particularly useful in understanding how elements interact in chemical reactions, especially in organic chemistry where silicon plays a role similar to carbon due to its ability to form four bonds.