Give preparation of phosphine (`PH_3`).

Explanation

Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
`Ca_(3)P_(2) + 6H_(2)O to 3Ca(OH)_(2) + 2PH_(3)`
`Ca_(3)P_(2) + 6HCl to 3CaCl_(2) + 2PH_(3)`
In laboratory, it is prepared by heating white phosphorous with concentrated NaOH solution in an inert atmosphere of `CO_(2)`
`P_(4) + 3NaOH + 3H_(2)O to underset("Sodium hypophosphite")(PH_(3) + 3NaH_(2) + PO_(2))`
When pure, it is non inflammable but becomes inflammable owing to presence of `P_2H_4` or `P_4` vapours. To purify it from the impurities it is absorbed in HI to form phosphonium iodide (`PH_4I`) which on treatment with KOH gives off phosphine:
`PH_(4)I + KOH to Kl + H_(2)O + PH_(3)`