JEE Advanced 2017 · Paper 2 · Chemistry Q4

ChemistrySingle correct+3 / -1Question 22 of 54

Which of the following combination will produce $\ce{H2}$ gas?

Fe metal and conc.

\ce{HNO3}

Cu metal and conc.

\ce{HNO3}

Zn metal and NaOH(aq)

Au metal and NaCN(aq) in the presence of air

Answer and worked solution

Official answer: C

(A) Fe is passivated by concentrated $\ce{HNO3}$ , and in any case gives oxides of nitrogen, not $\ce{H2}$ .
(B) $\ce{Cu}$ with concentrated $\ce{HNO3}$ gives $\ce{NO2}$ .
(C) Amphoteric zinc releases hydrogen with alkali: $\ce{Zn + 2NaOH + 2H2O -> Na2[Zn(OH)4] + H2}$ . ✓
(D) Au with NaCN in air forms $\ce{[Au(CN)2]-}$ . Oxygen is reduced to $\ce{OH-}$ ; no $\ce{H2}$ is formed.

(C)

Topics:Group 15 Transition element properties

JEE Advanced 2017 · Paper 2, Chemistry question 4