Difference between Gas and Vapour:
Gas:
A thermodynamic state in which a substance exists only in one phase i.e. Gas phase. In above given examples N₂, He and CO₂ exists as gases at room temperature. These gases cannot form a solid or liquid phase along with gas phase as these states requires very low temperatures.
Vapours:
It is a thermodyanamic state in which a substance exists in more than one phase. In given options Sulfur can exist in vapor state. This is because sulfur exists in a cyclic or chain form due to catenation (self linkage property). Therefore, a lower members of S allotrops can form a vapours.
<u>Answer:</u> The correct answer is Option b.
<u>Explanation:</u>
Reducing agents are defined as the agents which help the other substance to get reduced and itself gets oxidized. They undergo oxidation reaction.

For determination of reducing agents, we will look at the oxidation potentials of the substance. Oxidation potentials can be determined by reversing the standard reduction potentials.
For the given options:
- <u>Option a:</u>

This ion cannot be further oxidized because +1 is the most stable oxidation state of silver.
- <u>Option b:</u>

This metal can easily get oxidized to
ion and the standard oxidation potential for this is 0.13 V

- <u>Option c:</u>

This metal can easily get oxidized to
ion and the standard oxidation potential for this is 0.0 V

- <u>Option d:</u>

This metal can easily get oxidized to
ion and the standard oxidation potential for this is -0.80 V

- <u>Option e:</u>

This ion cannot be further oxidized because +2 is the most stable oxidation state of magnesium.
By looking at the standard oxidation potential of the substances, the substance having highest positive
potential will always get oxidized and will undergo oxidation reaction. Thus, considered as strong reducing agent.
From the above values, the correct answer is Option b.
When an electron absorbs energy, it will move up from a lower energy level to a higher energy level, called the "excited state" of the negatively-charged subatomic particle.<span> However, the absorbed energy is released within a small interval of time and the electron moves down to its "ground state."</span>
Answer:
I believe Na
Explanation:
Copper, because it is the only metal out of all of them.
Therefore copper is the only element that can loose electrons to have a positive charge, it is the most likely to become a cation.