What is the valence of phosphorus (P) in the compound P4O10?

In the compound P4O10, phosphorus exhibits a valence of +5. To understand this, let's consider the overall structure and composition of the compound.

P4O10 consists of four phosphorus atoms and ten oxygen atoms. Oxygen typically has a valence of -2. When tallying the overall negative charge contributed by the ten oxygen atoms in P4O10, this amounts to a total of -20 (10 x -2 = -20).

To achieve charge balance in the compound, the total positive charge from the phosphorus atoms must equal the total negative charge from the oxygens. Since there are four phosphorus atoms, we can denote their valence as x. The equation then looks like this:

4x (from phosphorus) + (-20) (from oxygen) = 0

Solving for x gives:

4x - 20 = 0

4x = 20

x = +5

Thus, each phosphorus atom in P4O10 has a valence of +5, leading to the conclusion that the answer is indeed +5. This reflects phosphorus' ability to expand its valence shell and form multiple bonds, particularly with highly electronegative atoms like oxygen.