(I) Molecular mass: 

1. Relative molecular mass is defined as the ratio of the mass of the molecule to the unified atomic mass unit. 

2. It can be calculated by adding the relative atomic masses of its constituent atoms. 

3. For carbon monoxide (CO)

Molecular mass = Atomic mass of carbon + Atomic mass of oxygen 12 + 16 = 28 u.

Molar mass: 

1. It is defined as the mass of one mole of a substance. 

2. The molar mass of a compound is equal to the sum of the relative atomic masses of its constituent expressed in g mol . 

3. For carbon monoxide (CO)

12 + 16 = 28 g mol^-1.

Both molecular mass and molar mass are numerically same but the units are different.

(II) These are the reactions in which redox reactions take place in different vessels and it is an indirect redox reaction. There is a competition for the release of electrons among different metals.

Example: 

Zn releases electrons to Cu and Cu releases electrons to Silver and so on. 

Zn_(s) + Cu²⁺ → Zn²⁺ + Cu_(s) (Here Zn – oxidised; Cu²⁺ – reduced) 

Cu_(s) + 2Ag⁺ → Cu²⁺_(aq) + 2Ag_(s) (Here Cu – oxidised; Ag⁺ – reduced)