Answer: D) 36 yrs Explanation: Let present ages of Sumit=w, Krishna=x, Rishabh=y and Rohit=z , thenw+x+y = 43x3 = 129 ---(i) andw+y+z = 49x3 = 147 ---(ii)Subtracting (i) from (ii), (w+y+z) - (w+x+y)=147 -129 , z- x =18 ---(iii)Given Rohit's age => z = 54, so from (iii), x = 54-18 = 36

Answer: C) H2O Explanation: The common greenhouse gas containing only hydrogen and oxygen is H2O, this is water vapor. The common greenhouse gases are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. The composition (chemical formula) of those gases are: Water vapor: H2OCarbon dioxide: CO2Methane: CH4Nitrous oxide: NOOzone: O3. As you see the only one of those that contains only hydrogen and oxygen is H2O, water vapor.

Answer: B) Encryption Explanation: The coding or scrambling of data so that humans cannot read them is known as encryption.