Class 8 Science: What Decides Different States of Matter? — Practice Questions with Answers

Explanation: In solids, the particles are arranged very close to each other with very little empty space between them. This tight packing, along with strong forces of attraction, is why solids have a fixed shape and a fixed volume.

Explanation: Gas particles are very far apart and move about freely in all directions because the forces of attraction between them are negligible. So a gas spreads out to fill its entire container, taking both the shape and the volume of the container.

Explanation: In solids, the particles are held tightly at fixed positions by strong forces of attraction. These forces are weaker in liquids, where particles can slide past one another, and weakest in gases, where particles move about almost freely.

Explanation: In a liquid, the forces between particles are strong enough to keep them close together but not strong enough to hold them at fixed positions. The particles can slide over one another, so the liquid flows and takes the shape of its container.

Explanation: In a gas, the particles are very far apart, so there is a lot of empty space between them. On compressing, the particles are simply pushed closer into this empty space. In a solid, the particles are already packed closely, so there is almost no space left to squeeze them into. The particles themselves do not shrink.

Explanation: Heating gives energy to the particles of the solid, so they vibrate faster and faster about their positions. If enough heat is supplied, the vibrations become strong enough to overcome the forces of attraction, and the solid melts. The particles themselves do not grow in size or melt individually.

Explanation: In a solid, strong forces of attraction hold the particles tightly at fixed positions, where they can only vibrate. Since the particles cannot leave their positions, the solid keeps a definite shape. In liquids and gases, the particles can move around, so those states have no fixed shape.

Explanation: Gas particles are in constant, rapid and random motion. The fragrance particles from the incense stick mix into the spaces between the fast-moving air particles and quickly spread through the whole room. This mixing of particles on their own is called diffusion.

Explanation: Particles are most closely packed in the solid state, slightly farther apart in the liquid state, and very far apart in the gaseous state. So the interparticle space generally increases from solid to liquid to gas. This is also why gases can be compressed easily while solids cannot.

Explanation: X behaves like a liquid: the attraction between its particles is strong enough to keep them together, giving a fixed volume, but the particles can slide around, so it takes the shape of its container. Y behaves like a gas: the attraction between its particles is negligible, so it has neither a fixed shape nor a fixed volume. Hence the interparticle forces are stronger in X than in Y.

Explanation: Gas particles are far apart with large empty spaces between them, so the forces of attraction hardly act. On applying high pressure, the particles are forced very close together. At this small distance, the forces of attraction become effective enough to hold the particles together, and the gas changes into a liquid.

Explanation: The attraction between liquid particles is strong enough to keep them close together, so the liquid occupies a definite volume. But it is not strong enough to lock the particles at fixed positions, so they slide past one another and the liquid takes the shape of its container. One particle arrangement explains both properties.