# Yellow phosphorous on reaction with $Ca(OH)_2$ gives

$\begin{array}{1 1}(a)\;Ca(H_2PO_4)_2&(b)\;Ca(H_2PO_2)_2\\(c)\;PH_3&(d)\;both\;(b)\;and\;(c)\end{array}$

$8P+3Ca(OH)_2+6H_2O\rightarrow 3Ca(H_2PO_2)_2+2PH_3$
Hence Yellow phosphorous on reaction with $Ca(OH)_2$ gives $Ca(H_2PO_2)_2,PH_3$
Hence (d) is the correct answer.