DIRECTIONS for question 6-10: The following questions are based on the passage. Read each statement.
If the temperature of a gas is decreased sufficiently a stage will be reached when the speed of movement of the molecules is so reduced that become close enough to exert attractive forces on each other. These forces differ from the forces that hold the atoms together in a molecule, but they are also electrical in fact they result from the attraction between the positively charged nucleus of one atom and the negatively charged orbital electrons of atom in neighboring molecules such forces are called molecular forces (Vander wall forces, after the discoverer). At that point, in the process of reducing the temperature of a gas when the attractive forces between the molecules are sufficient to market the gas is said to have become a liquid. In contrast to solids however, the molecules of a liquid are still able to slide over one another, so that the bulk is able to adopt the shape of its container. Some of the more rapid molecules at the surface of a liquid are able to overcome the molecular forces of their neighboring molecules and escape from the liquid into the gas above it: this process is called evaporation. As it is the fastest moving molecules that escape, that is the molecules with the greatest energy, the average energy of the remaining molecules will be reduced, and hence the effect of evaporation is to cause a reduction in the temperature of the liquid. As a result of the continual escape of molecules from the surface of a liquid, the gas above it will contain a certain number of molecules of the liquid. This number will depend on the temperature and the chemical composition of the liquid. However, for a particular liquid, at a particular temperature, the average number of molecules escaping from the surface will always be the same, and the pressure these molecules exert is called the vapour pressure of the liquid. Mark (1) If the idea is stated in the passage; Mark (2) If the idea contradicts the contents of the passage; Mark (3) If the idea is not explicitly stated in the passage, but can be deduced from its contents; Mark (4) If the idea cannot be deduced from its content.
As the fast-moving molecules of a gas releases into a liquid, this process is called evaporation.
Answer: A This idea has been mentioned in the definition of evaporation
Irrespective of the chemical composition of the gas, equal volumes of a gas the same temperature and pressure always contain the same number of molecules.
Answer: C The idea is only deducable. Has not been mentioned directly. Thus, the correct answer should be option 3
Vapour pressure is the total pressure exerted by the molecules of a gas on the surface of a liquid below it.
Answer: C It is clearly stated in the last line of the passage.
Evaporation increases as the surface area of a liquid increases.
Answer: D No information is given in the passage.
There is no relation between the reduction of temperature of a gas and the attraction between its molecules.
Answer: B From the 1st para it is clear that there is relation between reduction of temperature of a gas and the attraction between its molecules.