Answer:
The average pressure in the container due to these 75 gas molecules is 
Explanation:
Here Pressure in a container is given as

Here
- P is the pressure which is to be calculated
- ρ is the density of the gas which is to be calculated as below

Here
mass is to be calculated for 75 gas phase molecules as

Volume of container is 0.5 lts
So density is given as

is the mean squared velocity which is given as

Here RMS is the Root Mean Square speed given as 605 m/s so

Substituting the values in the equation and solving

So the average pressure in the container due to these 75 gas molecules is 
D. radioactive isotopes are one of the environmental waste products of nuclear energy.
Answer:
Burning of paper is not a physical change.It is chemical change as ash is formed in the process which is new compound and oxides of carbon are also released during the process!
Answer:
Iodide> Bromide > chloride > flouride
Explanation:
During a nucleophilic substitution reaction, a nucleophilie replaces another in a molecule.
This process may occur via an ionic mechanism (SN1) or via a concerted mechanism (SN2).
In either case, the ease of departure of the leaving group is determined by the nature of the C-X bond. The stronger the C-X bond, the worse the leaving group will be in nucleophilic substitution. The order of strength of C-X bond is F>Cl>Br>I.
Hence, iodine displays the weakest C-X bond strength and it is thus, a very good leaving group in nucleophillic substitution while fluorine displays a very high C-X bond strength hence it is a bad leaving group in nucleophilic substitution.
Therefore, the ease of the use of halide ions as leaving groups follows the trend; Iodide> Bromide > chloride > flouride