Consider the following reaction :
$$A + alkali \to B$$ (Major Product)
If B is an oxoacid of phosphorus with no P - H bond, then A is

We are given that A reacts with alkali to give B (major product), where B is an oxoacid of phosphorus with no P-H bond. We need to identify A.

Identify the oxoacid B

The common oxoacids of phosphorus and their P-H bonds are:

- Hypophosphorous acid ($$H_3PO_2$$): has 2 P-H bonds

- Phosphorous acid ($$H_3PO_3$$): has 1 P-H bond

- Orthophosphoric acid ($$H_3PO_4$$): has no P-H bond (all three H atoms are bonded to oxygen)

Since B has no P-H bond, B must be orthophosphoric acid ($$H_3PO_4$$) or its salt.

Check each option

Option A: White $$P_4$$ with alkali

White phosphorus undergoes disproportionation with NaOH:

$$P_4 + 3NaOH + 3H_2O \to PH_3 + 3NaH_2PO_2$$

The major product is sodium hypophosphite ($$NaH_2PO_2$$), a salt of hypophosphorous acid ($$H_3PO_2$$), which has 2 P-H bonds. This does not match.

Option B: Red P with alkali

Red phosphorus, when heated with concentrated NaOH, undergoes disproportionation differently from white phosphorus. The reaction gives sodium phosphate as the major product:

$$8P + 12NaOH + 4H_2O \xrightarrow{\Delta} 4Na_3PO_4 + 2PH_3 + 2P_2H_4$$

The major product is $$Na_3PO_4$$ (sodium phosphate), which is a salt of orthophosphoric acid ($$H_3PO_4$$). Orthophosphoric acid has no P-H bond. This matches!

Option C: $$H_3PO_3$$ with alkali

$$H_3PO_3$$ is a dibasic acid that simply neutralizes with alkali:

$$H_3PO_3 + 2NaOH \to Na_2HPO_3 + 2H_2O$$

The product $$Na_2HPO_3$$ is the salt of phosphorous acid, which retains its P-H bond. Does not match.

Option D: $$P_2O_3$$ with alkali

$$P_2O_3$$ with water or alkali gives phosphorous acid:

$$P_2O_3 + 3H_2O \to 2H_3PO_3$$

Phosphorous acid has 1 P-H bond. Does not match.

Conclusion

Only Red P, when heated with concentrated alkali, produces sodium phosphate ($$Na_3PO_4$$), a salt of $$H_3PO_4$$ -- an oxoacid with no P-H bond.

The correct answer is Option B: Red P.