Ans. Anything which has mass and volume is called matter.

Ans. Matter is made up of particles.

Ans. Particles are the smallest part of any matter which cannot be broken further.

Ans. Particles of a matter have the following characteristics:

• Particles of matter have space between them.
• Particles of matter are continuously moving or they possess kinetic energy.
• Particles of matter attract each other.

Ans. There are mainly three physical states of a matter:

• Solid
• Liquid
• Gas

Ans. The matter which has fixed shape and fixed volume is called solid state.

Ans. The matter which does not have fixed shape but fixed volume is called liquid state.

Ans. The matter which neither has a fixed shape nor fixed volume is called gas state.

Ans. A solid has the following properties:

• The space between the particles is minimum.
• The kinetic energy is minimum.
• The force of attraction between the particles is maximum.

Ans. A liquid has the following properties :-

• The space between the particles is medium.
• The kinetic energy is medium.
• The force of attraction between the particles is medium.

Ans. A gas has the following properties:

• The space between the particles is maximum.
• The kinetic energy is maximum.
• The force of attraction between the particles is minimum.

Ans. Kinetic energy is the energy of a matter due to its motion.

Ans. It is the ability of a matter by which it can decrease its volume when the force is applied. This ability is only found in the gas state.

Ans. Intermixing of particles of two different types of matter on their own is called diffusion.

Ans. The temperature and the kinetic energy of the particles are directly proportional to each other. If we increase the temperature of a matter, the kinetic energy of the particles also increases and vice versa.

Ans. The temperature and the rate of diffusion of the particles are directly proportional to each other. It means, if we increase the temperature of a matter, the rate of diffusion of the matter’s particles also increases and vice versa.

Ans. Hot food has a higher temperature than cold food so it has higher kinetic energy as well as higher rate of diffusion than cold food. Because of these, particles of the hot food diffuse faster in air and move fastly and reach several meters away.

Ans. A diver is able to cut through water in a swimming pool because there is enough space and less force of attraction between the particles of water.

Ans. Rigidity is the ability of a matter to resist change in its shape. Solids are generally rigid.

Ans. Fluidity is the ability of a matter by which it can flow. Liquid and gas are generally fluid.

Ans. Filling a gas container means gas is increasing the space between its particles and hence increasing its volume and attains the shape of the container.

Ans. Shape is the boundary of a matter.

Ans. Density is the mass per unit volume of a matter. Its SI unit is Kg/m³.

Ans. The gas has no fixed volume because it can increase or decrease the space between its particles according to the container in which it is kept and hence fills it completely.

Ans. A gas has higher kinetic energy and hence its particles move vigorously and it increases the space between its particles and tries to increase its volume and while doing so the gas exerts pressure on the walls of the container.

Ans. A wooden table should be called a solid because its shape and volume are fixed, which can only be seen in the solid state.

Ans. We can easily move our hands in air because air is in gas state in which the force of attraction between the particles is very less and we can easily overcome this force but to do the same in a solid block of wood we need a karate expert because in the solid, the force of attraction between its particles is very high and overcoming it is not so easy.

Ans. Liquids generally have lower density as compared to solids but this is not true in the case of water and ice. Ice has lower density than water because the air trapped inside the ice while freezing increases its volume and density of a matter is inversely proportional to the volume of the matter.

Ans. Yes, we can change the state of a matter. There are two methods of doing so:

1. By changing the temperature
2. By changing the pressure

1. Fusion: The change of solid state into liquid state is called fusion.
2. Vaporization: The change of liquid state into gas state is called vaporization.
3. Condensation: The change of gas state into liquid state is called condensation.
4. Solidification: The change of liquid state into solid state is called solidification.
5. Sublimation: The change of solid state directly into gas state is called sublimation.
6. Deposition: The change of gas state directly into solid state is called deposition.

Ans. During the change of state the given temperature is used in overcoming the force of attraction between the particles of a substance to change the state of matter, hence the temperature remains constant during the change of state.

Ans. The amount of heat energy that is required to change 1 kg of a solid into liquid without changing the pressure at its melting point is known as the latent heat of fusion.

Ans. The amount of heat energy that is required to change 1 kg of a liquid into gas without changing the pressure at its boiling point is known as the vaporization heat of fusion.

Ans. The minimum temperature at which a solid starts melting at atmospheric pressure is known as its melting point.

Ans. The minimum temperature at which a liquid starts boiling at atmospheric pressure is known as its boiling point.

Ans. To convert water into ice, we have to decrease the temperature and during the change of state it does not show the decreased temperature because it is hidden in the ice as latent heat. Therefore, ice absorbs more heat from the surroundings and is colder than water at the same temperature.

Ans. The SI unit of temperature is Kelvin.

Ans. To change Celsius to Kelvin, simply add 273 to the given temperature.

Ans. To change Kelvin to Celsius, simply subtract 273 from the given temperature.

Ans. The matters which directly convert into solid to gas or vice versa are called sublimable matters. For example: Naphthalene, camphor, dry ice (Solid CO₂).

Ans. Atmospheric gases can be converted into liquid by increasing pressure and decreasing temperature.

Ans. When any liquid changes into gas without reaching its boiling point, it is called evaporation.

Ans. The rate of evaporation depends on the following factors:

1. Surface Area: As surface area increases, the rate of evaporation increases and vice versa.
2. Temperature: Increase in temperature increases the rate of evaporation.
3. Humidity: Increase in humidity decreases the rate of evaporation.
4. Wind Speed: Increase in wind speed increases the rate of evaporation.

Ans. When any liquid evaporates it needs energy, which it gains from the surrounding. As the surrounding loses its energy, it becomes cool and causes a cooling effect.

Ans. During summer, our body sweats a lot and the sweat is absorbed better by cotton. The absorbed sweat takes energy from our body to evaporate and as our body loses energy it becomes cool and makes us comfortable during summer.

Ans. Ice-cold water cools the surrounding atmospheric air. When air is cooled, it condenses to form water. Hence, the surrounding air converts into water droplets which are seen on the outer surface of the glass.

Ans. Water is poured in a desert cooler and released as tiny droplets. These droplets gain energy from the surroundings to evaporate. As the surrounding loses energy, it becomes cool.

Ans. An earthen pot has tiny pores on its surface. Water leaks through these pores and evaporates by taking energy from the surroundings. As the surroundings lose energy, cooling takes place and the water inside the pot remains cool.

Ans. Acetone, petrol and perfume evaporate easily even at low temperatures. When applied on the palm, they take energy from the skin to evaporate. As the palm loses energy, it feels cold.

Ans. A saucer has a larger surface area than a cup. Hence, the rate of evaporation is higher in a saucer. Evaporation causes cooling, so tea or milk cools faster in a saucer.

Ans. Naphthalene balls are sublimable substances. They directly convert from solid to gas at room temperature, so they disappear with time without leaving any solid.

Ans. Perfume easily evaporates at room temperature and changes into gas. In the gaseous state, its particles have high kinetic energy and move rapidly, due to which the smell spreads several meters away.

Ans. Water at room temperature is a liquid because:

1. Room temperature is lower than its boiling point, so it does not convert into gas.
2. Room temperature is higher than its freezing point, so it does not convert into solid.

Ans. An iron almirah is a solid at room temperature because:

1. Room temperature is much lower than its boiling point, so it cannot convert into gas.
2. Room temperature is lower than its melting point, so it cannot convert into liquid.

Ans. Ice at 273 K absorbs additional heat from the surroundings to change into water because it has latent heat of fusion. Therefore, ice absorbs more heat than water at the same temperature and is more effective in cooling.

Ans. Steam produces more severe burns than boiling water because steam contains latent heat of vaporisation and releases extra heat when it condenses on the skin.