6. All the following are oxidation-reduction reactions except A) B) C) D) E) H2(

Question

6. All the following are oxidation-reduction reactions except A) B) C) D) E) H2(g)+F2(g) 2HFig). 6Li(s) + N2(g) -* 2LiN(s). Ca(s) +H-(g) CaH2(s). Mg,N2(s) +6H20(/) 3Mg(OH)2(s) +2NH3(g). 2K(s) +2H20(1) 2KOH(aq) + H2(g). 7. The oxidation numbers of nitrogen in N:0 and N F4 are, respectively, A) _2 and _3 B)-2 and +2 c) +1 and-1 D) +1 and +2. E) +1 and-3. 8. For the reaction that occurs in a lead storage battery Pbis) + PbO2(s) + 2H'(aq) the oxidizing agent is A) Pb. B) PbO C) H D) HSO4 E) PbSO 2Hso. (aq) 2PbSOds) + 2H20(/) 9. In the balanced equation the reducing agent is A) Na B) OH C) PH E) H:O 10. All of the following reactions are described as decomposition reactions except A) B) C) D) E) (NH4)2Cr20;(s) N2(g) +4H20(g) + Cro3(s). NH4HS(s) NHAg)+H2S(g). 2CH:OH(/) + 3O2(g) 2COdg)-4H20(g). PCIs(/) PCI3(g) + Cl2(g). 2COtg) 2CO(g) +02(g). Page 2

Explanation / Answer

Q.6: Option (D) is not an oxidation - reduction reaction. Because the oxidation state of magnesium is +2 in both the reactant and the product. Also the oxidation state of nitrogen is -3 in both the reactant and product side. Hence neither oxidation nor reduction takes place. Hence option (D) is correct.

Q.7: In N2O, OS of O is -2

=> 2x - 2 = 0

=> x = 2/2 = +1

Hence OS on N in N2O is +1.

In N2F4, OS of F is -1

=> 2x + 4 x (-1) = 0

=> x = 4/2 = +2

Hence OS on N in N2F4 is +2.

Hence option (D) is correct.

Q.8: An oxidizing agent helps in oxidation and itself get reduced.

The OS of Pb in PbO2(s) is +4. During the reaction the OS of Pb is decreased from +4 (in PbO2) to +2 (in PbSO4). Hence PbO2(s) gets reduced during the reaction and acts as oxidizing agent.

Hence option (B) is correct.

Q.9: A reducing agent helps in reduction and itself gets oxidized.

Here P4 is oxidized from 0 to +1 ( in H2PO2-) in the prodcut. Hence P4 is the reducing agent.

Hence option (D) is correct.

Q.10: Option (C) is a combustion reaction in which CH2OH is oxidized to form H2O and CO2. Hence option (C) is correct.

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