Class 9 Science Chapter 1 MCQ

Option C is correct because Hydrogen gas leaking from the container leaves some vacant space inside the container. So, hydrogen gas molecules inside the container occupy all the space available and the distance between the molecules of hydrogen gas will be increased. On increasing the volume of the container of hydrogen gas, more space will be available inside the container and hydrogen gas molecule will occupy all the space available and hence distance between the molecules will be increased. On increasing pressure, hydrogen molecules will come closer and the distance between them will be decreased. More hydrogen gas molecules are available in less volume, so the distance between them will be decreased.

The bromine vapor is heavier than air. And rest of all statement are correct. Hence, your answer will be option [D].

During melting, temperature of the ice does not change at all because the heat is used in overcoming the particle-particle attraction forces, which in turn keeps the temperature constant.

The correct order of boiling points of diethyl ether, acetone and n-butyl alcohol in kelvin scale is 308 K, 329 K and 391 K, which can be explained as: Boiling point of diethyl ether = 35 degree Celsius + 273 = 308 K Boiling point of acetone = 56 degree Celsius + 273 = 329 K Boiling point of n-butyl alcohol = 118 degree Celsius + 273 = 391 K

When a few crystals of copper sulphate are placed at the bottom of a beaker containing water, then water in the whole beaker turns blue slowly.

At 0°C, water releases some heat to lower the speed of molecules, and when it is cool enough the molecules of water are fixed at one position and they start vibrating. Ultimately, the water molecules convert into ice (solid).

Conversion of solid into vapours on heating or vapours into solid on cooling without undergoing in liquid state is called sublimation. The conversion of liquid into gas or vapour is called vaporization. The conversion of liquid into solid is called freezing. The conversion of solid into liquid is called melting.

Here, all the statements are correct. Hence, your answer will be option [D].

Temperature of the water during vaporisation does not change at all because the heat is used in overcoming particle-particle attraction forces, which in turn keeps the temperature constant.

Here, all the statements are correct. Hence, your answer will be option [D].

When surface area increases and temperature rises, evaporation of water increases because the area which is exposed to the outer atmosphere is more and increasing the temperature leads to increase in the kinetic energy, due to which rate of evaporation increases.

During summer, water kept in an earthen pot becomes cool because of the phenomenon of evaporation. Earthen pot has a large number of tiny pores in its walls and some of the water molecules continuously keep seeping through these pores to outside the pot. This water evaporates continuously and take the latent heat required for vaporization from the remaining water. In this way, the remaining water loses heat and gets cooled. Note: i) Diffusion is the net spreading out movement of a substance from a region of high concentration to a region of low concentration and mixing of a substance with another substance due to motion of its particles. ii) Transpiration is the process of water movement through a plant and its evaporation from aerial parts such as leaves. iii) Osmosis is the process in which solvent molecules move from their higher concentration to their lower concentration through semi permeable membrane. iv) Evaporation is the process in which a liquid changes into vapour or gas even below its boiling point.

Here, all the statements are correct. Hence, your answer will be option [D].

Ammonia gas can be liquefied by applying high pressure and lowering the temperature. In option [B]: Solid carbon dioxide is stored under high pressure. In option [C]: The conversion of solid carbon dioxide into carbon dioxide gas is a change of state which is caused by the decrease in pressure and increase atmospheric temperature. In option [D]: Whatever be the temperature at which evaporation take place, the latent heat of vaporization must be supplied whenever a liquid change into vapour or gas.

The statement that the particles of bromine are moving but those of air are not moving is incorrect because the particles of matter are constantly in motion. It appears as if the air molecules are not moving because air is colourless.

Gases and liquids behave like fluids. Both gases and liquids tend to flow due to less force of attraction between their particle. Also, they required vessel to keep them. Solids do not flow. Note: Fluid means a material which can flow easily and requires a vessel to keep it.

With the help of experiments it can be shown that at low temperature and high pressures, gases will liquefy. Because these factors affect the interaction force of molecules i.e. the molecules are able to establish a force of attraction between them on lowering the temperature and increasing pressure.

Here, all the statements are correct. Hence, your answer will be option [D].

The process of changing a gas or vapour to a liquid by cooling is called condensation.

The process occurring here is diffusion and it is unaffected by the mass. Therefore, bromine being heavier, mixes with the colorless air.

The above answer is not true because in liquids the molecules are not arranged in regular pattern. In liquids the molecules are loosely arranged.

Here, all these statements are correct. Hence, your answer will be option [D].

Here, all these statements are correct. Hence, your answer will be option [D].

Once the water has begun to boil, the temperature remains constant at hundred degree Celsius until all the water has changed into steam.

It has been found that the burns caused by stems are much more severe than those caused by boiling water though both of them at the same temperature of 100 degree Celsius. This is due to the fact that steam contains more heat, in the form of latent heat, than boiling water. So, when stem falls on our skin and condensed to produce water it gives out 22.5 x 10 to the power 5 J/kg more heat than boiling water, at the same temperature. Since, steam gives out more heat than boiling water it causes more severe burns.