Question

The covalence of the central atom is maximum in
a)HCN
B)NH4+
C)PCl5
D)H2O

Answer 1

Answer:

Elements which have vacant d-orbital can expand their octet by transferring electrons, which arise after unpairing, to these vacant d-orbital e.g. in sulphur. . Thus an element can show a maximum covalency equal to its group number e.g. chlorine shows maximum covalency of seven.

Answer 2

ANSWER

First, note that covalency = number of bonds formed.

In HCN, the carbon atom forms 1 bond with hydrogen and 3 bonds with nitrogen so covalency = 4. In ammonium ion, nitrogen atom forms 1 bond with each hydrogen. So, covalency = 4. In phosphorus pentachloride, the phosphorus atom forms 1 bond with each chlorine atom. So, covalency = 5. In a water molecule, the covalency of oxygen = 2.

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