```Ans : (d)
191. The pH of water at 25° C is 7. When it is heated to 100°C the pH of water: [NDA 2004]
(a) increases
(b) remains same
(c) decreases
(d) decreases upto 50 °C and then it increases
Ans : (b)
192. Match the following:
A. Alpha-rays                   1.    Helium atoms that
have lost two
electrons
B.   Beta-rays                  2.    Stream of electrons
C.   Gamma-rays                 3.    High energy
Electromagnetic
A        B          C
(a)  3        2          1
(b)  2        1          3
(c)  1        2          3
(d)  3        1          2
Ans : (c)
193. Which one of the following is the correct arrangement in the decreasing order of the refractive indices of glass, diamond and water?
(a) Glass, water, diamond
(b) Water, glass, diamond
(c) Diamond, water, glass
(d) Diamond, glass, water
Ans : (d)
194. Perspiration is maximum when:
(a) temperature is low and air is dry
(b) temperature is low and air is humid
(c) temperature is high and air is dry
(d) temperature is high and air is humid
Ans : (d)
195. The quantity of" water vapour the atmosphere can hold:
(a) decreases with increase of temperature
(b) is independent of temperature
(c) increases with increase of temperature
(d) fluctuates with increase of temperature
Ans : (c)
196. It takes much longer to cook things in the hills than in the plains, because:
(a) atmospheric pressure is high in the hills and water boils at a higher temperature
(b) atmospheric pressure is lower and water boils at a lower temperature
(c) due to low atmospheric pressure in the hills the boiling point of water is raised and therefore water takes longer to boil
(d) the humid atmosphere in the hills absorbes a lot of heat, leaving very little for the cooking
Ans : (b)
197. As a man moves directly away from a steady source of sound at constant speed, the sound he hears will:
233
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