Which of the following statements is true?
a. in general, the solubility of a solid in water decreases with increasing temperature.
b. in general, the solubility of a gas in water decreases with increasing temperature.
c. the solubility of a gas in water usually increases with decreasing pressure.
d. the solubility of an ionic solid in water decreases with increasing temperature.

Option (b) is the correct answer.

Explanation:

The solubility of a gas is dependent on both pressure and temperature. When we increase the temperature for a gas, then its molecules tend to gain more kinetic energy.

Hence, there occurs more number of collisions between the gas molecules. As a result, intermolecular bonds tend to break down and the molecules of gas become able to escape out of the solution.

Whereas when we increase the pressure on a gas then its molecules come closer to each other. Due to which there will be more number of collisions will take place. Therefore, solubility of a gas increases with increase in pressure.

Thus, we can conclude that the statement in general, the solubility of a gas in water decreases with increasing temperature, is true.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.

it can be observed without changing the identity of the object.

it depends on what substance you're talking about as well as many other factors. in quantum mechanics, the observation of particles affects the observers ability to measure certain properties. for example: you can know the velocity of a particle, but you can't know it's position; or you can know it's position, but not it's velocity. it's like trying to find out where a grain of sand is by throwing other grains of sand at it. once you find out where it is, it's been moved. it's also like trying to find an answer to the question of whether or not a tree falling in a forest makes a sound if nobody is there to hear it. paradoxically, the only way to find out is to be there and hear it.