A for precipitate formation reaction.
B for precipitate dissolution reaction.
C for precipitate exchange reaction.
D for no reaction.
${P_4} + NaOH \longrightarrow P{H_3} \uparrow + Na{H_2}P{O_2}$
${P_4} + 6Cl_2\xrightarrow{\Delta }PC{l_3}$