Question

7.
Four student used the following four combinations of reactants to observe the properties of
HCl and NaOH.They would observe a black residue in the test tubes :
I. Zn and dil. NaOH solution
II. Zn and dil. Hal solution
III. Na, CO3 and dil. NaOH solution
IV. NA CO and anl. HCl solution
There would be a rapid evolution of a gas in cases stated by response
Scho
a) I and I
b) II and IV
C) I and IV
d) I and III​

Answer 1

The option (c) is correct answer.

Explanation:

• Option (c) is the correct answer because rapid evolution of gas takes place in I and IV.
• In (I) Zn is added to dil.NaOH solution, releasing hydrogen gas. When metals are added to dil. NaOH solution they displace the Na and hydrogen gas is liberated.
• In (IV) sodium carbonate is added to dil. HCl hence liberating carbon dioxide in the reaction.