Question

Statement (I): Water containing less than 2000 ppm if dissolved solids can generally be used satisfactory for making concrete.

Statement (II): The presence of any of zinc, manganese, tin, copper or lead reduces the strength of concrete considerably. 
1. Both Statement (I) an Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) 
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I) 
3. Statement (I) is true but Statement (II) is false 
4. Statement (I) is false but Statement (II) is true 

Answer 1

Correct Answer - Option 2 : Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I) 

Statement 1: True

Clause number 5.4 and table 1 of IS 456: 2000 specifies the permissible limit of different constituents in the water which is to be used for mixing and curing of concrete. The permissible limit for dissolved solids in the water for satisfactory making of concrete is 2000 mg/lit or 2000 ppm. A higher concentration affects certain cement adversely.

Statement 2: True

The presence of zinc, manganese, tin, copper and lead considerably reduce the concrete strength. Because in presence of water zinc, manganese, tin, copper, and lead trend to react with sulphate and chloride which may present in cement and form inorganic salts which effect the strength development of concrete considerably. Like Zinc chloride retards the set of concrete and the 3-day strength test cannot be performed.

But, there are no cause-effect relations between these two statements, so statement 2 is not the correct explanation of statement 1.