Redox Reactions

36. Oxidation number ofS in S₂O₈^-2 is

(a) -2           (b) -6           (c) +2          (d) +6

36. Oxidation number ofS in S₂O₈^-2 is

32. Assertion: Na⁺ ion has an oxidation number of +1, Mg²⁺ ion, +2, Fe³⁺ ion, +3, Cl^– ion, –1, O^2– ion, –2; and so on.

Reason: For ions composed of only one atom, the oxidation number is equal to the charge on the ion.

Dinitrogen and dioxygen are main constituents of air, but these do not react with each other to form oxides of nitrogen because _________. 
(i) The reaction is endothermic and requires very high temperatures. 
(ii) The reaction can be initiated only in presence of a catalyst. 
(iii) Oxides of nitrogen are unstable. 
(iv) N₂ and O₂ are unreactive. 

The gaseous envelope around the earth is known as the atmosphere. The lowest layer of this is extended up to 10 km from sea level, this layer is _________. 
(i) Stratosphere 
(ii) Troposphere 
(iii) Mesosphere 
(iv) Hydrosphere 

Which of the following statements about photochemical smog is wrong? 

(i) It has a high concentration of oxidizing agents. 

(ii) It has a low concentration of oxidizing agents. 

(iii) It can be controlled by controlling the release of NO₂ , hydrocarbons, ozone etc. 

(iv) Plantation of some plants like Pinus helps in controlling photochemical smog.

Sewage containing organic waste should not be disposed of in water bodies because it causes major water pollution. Fishes in such a polluted water die because of 
(i) Large number of mosquitoes. 
(ii) Increase in the amount of dissolved oxygen. 
(iii) Decrease in the amount of dissolved oxygen in water. 
(iv) Clogging of gills by mud. 

Which of the following statements is wrong? 
(i) Ozone is not responsible for the greenhouse effect. 
(ii) Ozone can oxidize Sulphur dioxide present in the atmosphere to Sulphur trioxide. 
(iii) Ozone hole is thinning of the ozone layer present in the stratosphere. 
(iv) Ozone is produced in the upper stratosphere by the action of UV rays on oxygen. 

Biochemical Oxygen Demand (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water sample to be __________.
(i) Rich in dissolved oxygen. 
(ii) Poor in dissolved oxygen. 
(iii) Highly polluted. 
(iv) Not suitable for aquatic life. 

Which of the following statements is not true about classical smog?
(i) Its main components are produced by the action of sunlight on emissions of automobiles and factories. 
(ii) Produced in cold and humid climates. 
(iii) It contains compounds of reducing nature. 
(iv) It contains smoke, fog, and Sulphur dioxide.