Which of the following is the strongest base in an aqueous solution?

The reaction of $N,N'$-diphenylthiourea with concentrated $HCl$ upon heating is given by:
$(C_6H_5NH)_2C=S \xrightarrow{conc. HCl, Heat} A + B$
The unknown compounds $A$ and $B$ in the above reaction are:

Consider the three aromatic molecules ($P$, $Q$ and $R$) whose structures are given below. The correct order regarding the reactivity of these compounds with $Ph-N\equiv N^{(+)}Cl^{(-)}$ under optimum but slightly acidic medium is:

Identify substrate $A$ in the following conversion.
$A + \underset{\text{(excess)}}{CH_3 I} \xrightarrow{\Delta} C_2 H_5(CH_3)_3 N^+ I^-$

The major product of the reaction is:

The correct statement regarding the basicity of arylamines is