Why is `NH_2` group of aniline acetylated before carrying out nitration?

How is the activation of benzene ring by amino group reduced by acetylating aniline during nitration ?

Acylation of — NH_2 group in aniline reduces its reactivity in electrophilic substitution reactions.

Which of the indicated relationship is correct for the following exothermic reaction carried out at constant pressure? CO(g) +3H_(2)(g ) rarrCH_(4)(g)+H_(2)O(g)

Two long straight, current-carrying condcutors , PQ and XY, are held a constant distance apart as shown in the figure. The conductors carry the magnitude of current in the same direction . A plan view form above the conductors is shown in the figure. The magnetic flux density B at a distance d from a long straight wire carrying a current I is given by B = 2.0 xx 10^-7 I/d Use this expression to explain why, under normal circumstances, wires carrying alternating current are not seen to vibrate.

How many -NH_2 groups are found in a basic amino acid?