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. 

How many of these compounds will undergo disproportionation on hydrolysis? CO?, NO?, Cl?, F?, ClO?, Cl?O?, N?O?, SO?, P?O??

40. Best reducing agent is:
(a) He              (b) Be           (c) Li            (d) Al

37. Which element is considered to have oxidation number of +3 in all its compounds?

(a) Be              (b) Li             (c) Al         (d) Sc

36. Oxidation number ofS in S₂O₈^-2 is

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

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.