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heat capacity of H_{2}O at its boiling point is

1) 3 cal mol^{} ^{-1}K^{-1}

2)5 cal mol^{-1} ^{}K^{-1}

3) 7 cal mol^{-1} ^{}K^{-1}

4) Infinite

ANS : 4) how?

Heat capacity of a system is defined as the quantity of heat required to raise the temperature of the system by one degree.

$\mathrm{Heat}\mathrm{capacity}=\frac{\mathrm{dq}}{\mathrm{dT}}$

Boiling point of water = 100º C

Heat capacity of water will be the amount of heat required to raise the temperature from 100º C to 101 º C. At 100º C the temperature of the water becomes constant even after the addition of infinite amount of heat. This is because the heat supplied after attaining 100º C is utilised in changing the phase of water from liquid to vapour . This is called as latent heat. Therefore the amount of heat supplied is constant i.e. q=∞ and hence heat capacity becomes infinite.

**So, the answer is (d)**

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