Order of acidic nature

Which among the following compounds has the highest melting point?

Consider the following reaction:
The product $'P'$ gives a positive ceric ammonium nitrate test. This is because of the presence of which of these $-OH$ group$(s)$?

The reactivity of compound $Z$ with different halogens under appropriate conditions is given below:
(Image of reaction: $Z$ ($3$-tert-butylphenol) reacts with $X_2$ to give mono-halo derivative for $X_2 = I_2$,di-halo for $X_2 = Br_2$,and tri-halo for $X_2 = Cl_2$)
The observed pattern of electrophilic substitution can be explained by:
$A$. The steric effect of the halogen
$B$. The steric effect of the tert-butyl group
$C$. The electronic effect of the phenolic group
$D$. The electronic effect of the tert-butyl group

In which of the following,ortho/para substitution by an electrophile is very facile?

What is the natural source of salicylic acid?