Water at `0^@C` was heated until it started to boil and then until it all changed to steam. The time required to heat water from `0^@C` to `100^@C` is 5 min and the time to change boiling water to steam is 28 minutes. If the flame supplied heat at a constant rate, the specific latent heat of vaporisation of water (neglecting heat losses, container etc. is (in `J//g`). (specific heat of water s `=4.2 J//g` )

Options

A. 540
B. 2268
C. 2352
D. 2356

Answer

C

Explanation

Let heat is supplied at constant rate P,
For `0^@C` to `100^@C`
`Pxx(5xx60)=mxx4.2xx(100-0)` .(i)
For boiling: `Pxx(28xx60)=mL` ..(ii)
From (i) and (ii)
`L=(4.2xx100)xx(28)/(5)=2352 J//g`