In Lassaigne's test for halogens, it is necessary to remove $\text{'}\mathrm{X}\text{'}$ and $\text{'}\mathrm{Y}\text{'}$ from the sodium fusion extract, if nitrogen and Sulphur are present. This is done by boiling the extract with $\text{'}\mathrm{Z}\text{'}$. Identify $\mathrm{X}, \mathrm{Y}$ and $\mathrm{Z}$.

The increasing order of acidic strength among the following compounds is

$\mathrm{I}$. Benzoic acid
$\mathrm{II}$. $4-$nitrobenzoic acid
$\mathrm{III}$. $3, 4-$dinitrobenzoic acid
$\mathrm{IV}$. $4-$methoxybenzoic acid

The following effect is known as___

In the following resonance structures, the curved arrow indicates that electrons are shifted from