1) Which of the following combination will produce H2 gas? A) Fe metal and conc. $HNO_{3}$ B) Cu metal and conc,$HNO_{3}$ C) Au metal and NaCN(aq) in the presence of air D) Zn metal and NaOH(aq) Answer: Option DExplanation:$Zn + 2NaOH\rightarrow Na_{2}ZnO_{2}+H_{2}$
