A calorimeter of water equivalent $20 \mathrm{g}$ contains $180 \mathrm{g}$ of water at $25°\mathrm{C}$. ${}^{\text{'}}\mathrm{m}^{\text{'}}$' grams of steam at $100°\mathrm{C}$ is mixed in it till the temperature of the mixture is $31°\mathrm{C}$. The value of ${}^{\text{'}}\mathrm{m}^{\text{'}}$ is close to (Latent heat of water$=540 \mathrm{cal} {\mathrm{g}}^{-1}$, specific heat of water$=1 \mathrm{cal} {\mathrm{g}}^{-1°}{\mathrm{C}}^{-1}$)

• Correct answer
  A

  $2$
• B

  $4$
• C

  $3.2$
• D

  $2.6$

Hence, the correct answer is option: 'A'.