Question

The substance used as a smoke screen in war fare is

• A. $SiCl_4$
• B. $PH_3$
• C. $PCl_5$
• D. acetylene

Answer 1

Answer: (B)

$PH_3$

Answer 2

Actually, $P H _{3}$ is formed there along with acetylene under the reaction of $C a _{3} P _{2}$ with $C a C _{ 2 }$ where, the phosphene reacts with acetylene formed and catches fire to get smoke which forms the smoke screen. In Holme's signal, the calcium phosphide and calsium carbide is thrown in sea where the reaction produces phosphene gas and acetylene and the phosphene catches fire with acetylene and forms smoke which sends the signal. $C a _{3} P _{2}+ C a C _{2}-$ sea \rightarrow\left\\{ C _{2} H _{2}+ P H _{3}\right\\}