Which one of the following would raise the temperature of 20 g of water at `30^(@)C` most when mixed with?
(Specific heat of water is `1cal//g-.^(@)C`)

Options

A. 20 g of water at `40^@C`
B. 40 g of water at `35^@C`
C. 10 g of water at `50^@C`
D. 4 g of water at `80^@C`

Answer

D

Explanation

Let m grams of water whose temperature is `theta_0(gt30^@C)` and specific heat is `1 cal//g^(@)C` be added to 20 g of water at `30^@C` and let `theta` be the final temperature of mixture.
`m(1)(theta_0-theta)(20)(1)(theta-30)`
`theta=(600+mtheta_0)/(20+m)`
The right hand side is maximum for option (d). Therefore, the correct answer is (d)