calculate the mass of phosphorus required to make 200g of phosphine ,PH3 by the reaction:

Question

P4(S) +3NaOH(aq) +3H2O(I) �¨3NaH2PO4(aq) +PH3(g)

Answer 1

I think you mean 4P not P4
4P(S) +3NaOH(aq) +3H2O(I) �¨3NaH2PO4(aq) +PH3(g)

You need 4 P atoms on the left for every PH3 molecule on the right

atomic mass of P = 31
molecular mass of PH3 = 31+3 = 34
so every gram of PH3 has (31/34) grams of P
but we need 4 times that much to provide the other three in 3NaH2PO4
so for every gram of PH3 we need 124/34 grams of P
so
200 (124/34) = 729 grams of P