Which of the following molecule$(s)$ has/have delocalised lone pair$(s)$ of electrons?

Fill in the blanks:
$(1)$ In $+E$ effect,$\pi$ electrons from a multiple bond migrate to the ........... .
$(2)$ In $-E$ effect,$\pi$ electrons from a multiple bond migrate to the ........... .
$(3)$ ........... and ........... increase stability.
$(4)$ ........... inductive effect increases the acidic strength and ........... inductive effect decreases the strength of $-COOH$.

Identify the functional group that has electron donating inductive effect.

The decreasing order of reactivity towards electrophilic substitution for the following compounds is:

Explain the inductive effect with a suitable example.

Formic acid is a stronger acid than acetic acid. This can be explained using