Thermodynamics

Water freezes at a specific temperature and pressure. The phase change from liquid to solid occurs at a point known as the freezing point. Under standard atmospheric conditions:

Freezing Point: 0 ºC

Atmospheric Pressure: 1 atm

This is because the molecules in water slow down enough to form a crystalline structure, which results in the transition of water from a liquid state to solid ice. Therefore, considering the options provided, the correct conditions for the freezing of water are:

0 ºC, 1 atm

As a result, the freezing of water takes place in these conditions:

• Temperature of 0 ºC
• Atmospheric Pressure of 1 atm

The specific heat is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius (or Kelvin). It is a property that varies from one substance to another, meaning different substances require different amounts of heat to change their temperatures by the same amount. Hence, the statement "Its value is the same for all the substances" is false.

The other statements about specific heat are true:

• Its S.I. unit is J/kg-K. This is indeed correct as specific heat is measured by the amount of heat needed per kilogram of a substance per degree Kelvin.
• Its value is high when the rate of rise (or fall) of temperature is low. This is accurate because substances with high specific heat tend to change temperature slowly since they require more heat for the same temperature change.
• Its value for water is 1 cal/g-ºC. This is true for water, having one of the highest specific heat values, specifically 1 calorie per gram per degree Celsius, equivalent to 4.186 joules per gram per Celsius.

Therefore, the false statement is the first one, as specific heat indeed differs among various substances.

When wet cloths dry, the water in them seems to disappear. This phenomenon is caused by evaporation. Evaporation is the process where water changes from its liquid form to vapor or gas. This occurs when the molecules in the water gain enough energy to break free from the surface and enter the air.

Here's how it happens:

1. Heat Energy Absorption: The water molecules in the wet cloth absorb heat from the surroundings, which increases their kinetic energy.
2. Overcoming Intermolecular Forces: As their kinetic energy increases, these molecules can overcome the intermolecular forces holding them in the liquid state.
3. Changing State: When enough energy is gained, the molecules escape into the air as water vapor.
4. Dispersal: These vapor molecules mix with the air, effectively removing water from the cloth.

This process contrasts with other options such as freezing, condensation, and melting, which describe different phase changes of matter:

• Freezing: Liquid turning into a solid.
• Condensation: Gas turning into a liquid.
• Melting: Solid turning into a liquid.

Thus, the correct explanation for the disappearance of water from drying clothes is evaporation.