Question

Boiling point and melting point of a substance is 150 ${}^o$C and 50 ${}^o$C respectively. The temperature at which the substance undergoes freezing and condensation is X and Y respectively. Then:

• A. X < 150 ${}^o$C
  Y < 50 ${}^o$C
• B. X > 150 ${}^o$C
  Y > 50 ${}^o$C
• C. X = 150 ${}^o$C
  Y = 50 ${}^o$C
• D. X = 50 ${}^o$C
  Y = 150 ${}^o$C

Answer 1

The correct option is D X = 50 ${}^o$C

Y = 150 ${}^o$C
Conversion of physical state on heating:

$\text{Solid}\underrightarrow{melting}\text{Liquid}\underrightarrow{boiling}\text{Gas}$

Conversion of physical state on cooling:

$\text{Gas}\underrightarrow{condensation}\text{Liquid}\underrightarrow{freezing}\text{Solid}$

$\bullet$ Boiling point of a substance is the temperature at which it changes its state from liquid to gas. It is same as the temperature at which it condenses (i.e. changes from gas to liquid).
$\bullet$ Since boiling point of the given substance is 150 ${}^o$C, the temperature at which it condenses is 150 ${}^o$C, that is, Y = 150 ${}^o$C.

$\bullet$ Melting point of a substance is the temperature at which it changes its state from solid to liquid. It is same as the temperature at which it freezes.
$\bullet$ Since melting point of the given substance is 50 ${}^o$C, the temperature at which it freezes is 50 ${}^o$C, that is, X = 50 ${}^o$C.