The brown ring test for $NO_2^-$ and $NO_3^-$ ions is due to the formation of which of the following complex ions?

Which of the following statements is not correct?

The number of moles of $NH_{3}$ that must be added to $2 \, L$ of $0.80 \, M \, AgNO_{3}$ in order to reduce the concentration of $Ag^{+}$ ions to $5.0 \times 10^{-8} \, M$ ($K_{\text{formation}}$ for $[Ag(NH_{3})_{2}]^{+} = 1.0 \times 10^{8}$) is ...... . (Nearest integer)
[Assume no volume change on adding $NH_{3}$ ]

Which of the following complexes is the most stable?

$FeSO_4$ solution mixed with $(NH_4)_2SO_4$ solution in $1:1$ molar ratio gives the test of $Fe^{2+}$ ion,but $CuSO_4$ solution mixed with aqueous ammonia in $1:4$ molar ratio does not give the test of $Cu^{2+}$ ion. Explain why?

The $IR$ stretching frequencies of free $CO$ and $CO$ in $[V(CO)_6]^-$,$[Cr(CO)_6]$ and $[Mn(CO)_6]^+$ are $2143 \, cm^{-1}$,$1860 \, cm^{-1}$,$2000 \, cm^{-1}$ and $2090 \, cm^{-1}$,respectively. Then the correct statement about metal carbonyls is: