Question

Four students A, B, C and D were asked by their teacher to arrange the set-ups I to IV as given below and identify the gas, if any, evolved in each case :

After observation, the students arrived at the inferences recorded in the following table :

Students	I	I	III	IV
A B C D	Hydrogen Carbon dioxide Carbon dioxide No gas	No gas Hydrogen Hydrogen Carbon dioxide	Carbon dioxide No gas Hydrogen Carbon dioxide	Hydrogen Carbon dioxide No gas Hydrogen

The correct observations and inferences have been reported by the student :
(1) A
(2) B
(3) C
(4) D

Answer 1

In the setup I, sodium carbonate treated with dilute hydrochloric acid, it gives carbon dioxide and sodium chloride.
${\mathrm{Na}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)+2\mathrm{HCl}\left(\mathrm{aq}\right)\leftrightharpoons 2\mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{CO}}_2\left(\mathrm{g}\right)$
In setup II, when sodium hydroxide is treated with zinc, it gives zinc chloride and hydrogen gas will evolve.
$\mathrm{NaOH}\left(\mathrm{aq}\right)+\mathrm{Zn}\left(\mathrm{s}\right)\to {\mathrm{Na}}_2{\mathrm{ZnO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right)$
In setup III, when dilute hydrochloric acid reacts with zinc, it will give zinc chloride and hydrogen gas will evolve.
$\mathrm{Zn}\left(\mathrm{s}\right)+\mathrm{HCl}\left(\mathrm{aq}\right)\to {\mathrm{ZnCl}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{aq}\right)$
In setup IV, when sodium carbonate reacted with sodium hydroxide, no reaction takes place.

So, observations made by student C are correct.

Hence, the correct answer is option 3.