Explanation

(c)
This is also a mean of preparing alkene where the position of the double bond is definite. In Wittig reaction, aldehyde $( - CHO)$ and ketone $( > C = O)$ react with methylene tryphenyl phosphine $\lbrack\left( C_{6}H_{5} \right)_{3}P = CH_{2}\rbrack$ to give alkene.
$CH_{3}CHO + \left( C_{6}H_{5} \right)_{3}P = CH_{2}$
$\rightarrow CH_{3} - CH = CH_{2} + \left( C_{6}H_{5} \right)_{3}P = O$
Propane triphenyl phosphine
oxide
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