The metal ball can be considered  to be made up of several layers of thinner ones. On heating each of these layers will increase in radius. As the inner most layer also increases its radius, the volume inside it i.e, the volume of the hollow portion will also increase.

The resistance of metallic conductors e.g, platinum, increases with rise of  temperature . The increase in temperature results in a decrease of current which can be recorded in a galvanometer if the conductor is included in an electrical circuit. Thus the temperature can be known; platinum resistance thermometer is used generally for accurate scientific work. When two dissimilar metals are joined at the ends, and these ends are subjected to a difference of temperature, a current flows through the metals. Greater the difference of temperature , greater the current. So the curent strength can form the basis for measuring the difference in temperature. And when one of these temperatures is known, we can calculate the other.

Alcohol has a freezing point as low as -117oC. So it won't freeze even in very cold countries.

Before transferring the fish, the position is the man with the fish and the bucket of water. After transferring the position is : the man without the fish, but the fish inside the water in the bucket. Thus to know whether there is any change in weight, it is enough to consider whether there is any change in weight when the fish in air is transferred into the water. The answer is there is no change as when in water though it loses weight due to upthrust of water on it, the level of water increases and exerts an equal force at the bottom

The rapid flow of air between the two moving ships causes a reducton of pressure (Bernoulli's principle) , so they (the ships) are drawn closer together

The water rise in a capillary tube dipped in water is such that the weight of water in the tube above the surface of water in the vessel is equal to  the upward force due to surface tension. So it is clear that if the bore to the tube is decreased , the height of the water column in it  must be greater.

Cohesion refers to attraction between molecules of the same kind while adhesion refers to attraction between different kinds of molecules

Flows out of Newton's first law of motion.