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Q.
In aqua-regia the ratio of conc. $HNO _{3}$ and conc. $HCl$ present is :
AFMCAFMC 2003
Solution:
Aqua-regia is a mixture of conc. $HNO _{3}$ and conc. $HCl$ in the ratio $1: 3$.
Noble metals like gold and platinum are highly unreactive but react with aqua-regia forming respective chlorides
$\underbrace{ HNO _{3}}_{\text {aquaregia }}+3 HCl \longrightarrow \underset{\text { Nitrosyl chloride }}{ NOCl }+2 H _{2} O +2 Cl$
$Au +3 Cl \longrightarrow AuCl _{3}$
$Pt +4 Cl \longrightarrow PtCl _{4}$