The decreasing order of stability of the following anions is:
$(P)$ $p-OCH_3-C_6H_4-CH_2^-$
$(Q)$ $p-CHO-C_6H_4-CH_2^-$
$(R)$ $p-Cl-C_6H_4-CH_2^-$
$(S)$ $p-CH_3-C_6H_4-CH_2^-$

Given below are two statements,one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$ : Order of acidic nature of the following compounds is $A > B > C$.
(Image shows: $A$ is $2$-chlorocyclohexanol,$B$ is $4$-fluorocyclohexanol,$C$ is $3$-methylcyclohexanol)
Reason $R$ : Fluoro is a stronger electron withdrawing group than Chloro group.
In the light of the above statements,choose the correct answer from the options given below:

Which of the following is the most stable carbanion?

Which of the following is observed in the $C_2H_4$ molecule?

Which of the following structures possesses a cross-conjugated system?

Classify the following groups as electron-withdrawing ($-I$ effect) or electron-donating ($+I$ effect) inductive effect groups: $-CH_3, -Cl, -NO_2, -(CH_3)_3C, -OC_6H_5, -C_6H_5, -OH, -NH_2, -CH_2CH_3$.