Identify the $-I$ effect causing group from the following.

Identify ortho and para directing groups from the following: $I. -CHO$,$II. -NHCOCH_3$,$III. -OCH_3$,$IV. -SO_3H$.

Given below are two statements:
Statement $I$: In $O_2N-C_6H_4-CH^+-C_6H_4-OCH_3$, the carbocation is stabilised by $+R$ effect of $-OCH_3$ group.
Statement $II$: In $O_2N-C_6H_4-CH^--C_6H_4-OCH_3$, the carbanion is stabilised by $-R$ effect of $-NO_2$ group.
In the light of the above statements, choose the correct answer from the options given below:

The effect that makes $2,3-$dimethyl$-2-$butene more stable than $2-$butene is

Mesomeric effect involves

In which of the following molecules do all the effects namely inductive,mesomeric and hyperconjugation operate?