Question

when zn metal was dipped in a solution of acid, it released hydrogen gas. this reaction can be classified as
i. gas forming reaction
ii. single displacement reaction
iii. oxidation - reduction reaction
iv. acid - base reaction
v. combination reaction

1. i, iv and v
2. i, ii and iii
3. ii, iii and iv
4. i, iii and v

Explanation:

1. Gas - forming reaction: The reaction between Zn and acid produces \(H_2\) gas, so it is a gas - forming reaction (I is correct).
2. Single displacement reaction: The general reaction of a metal with an acid is \(Zn + 2H^+

ightarrow Zn^{2 +}+H_2\uparrow\), where Zn displaces \(H\) from the acid. This follows the pattern of a single displacement reaction (\(A+BC
ightarrow AC + B\)), so II is correct.

1. Oxidation - reduction reaction: In this reaction, the oxidation state of Zn changes from 0 to + 2 (oxidation), and the oxidation state of \(H\) in \(H^+\) changes from + 1 to 0 (reduction). Since there is a transfer of electrons (change in oxidation states), it is an oxidation - reduction reaction (III is correct).
2. Acid - Base reaction: An acid - base reaction involves the transfer of \(H^+\) from acid to base to form water and a salt. Here, the product is \(H_2\) gas and a salt of Zn, not water. So IV is incorrect.
3. Combination reaction: A combination reaction is of the form \(A + B

ightarrow AB\). The reaction between Zn and acid is not a combination reaction (V is incorrect).

So the correct classification is I, II, and III.

Answer:

1. I, II and III