Contrast exo. and endothermic reactions and give an example for each?

Explanation:

Endothermic reactions:

The type of reactions in which energy is absorbed are called endothermic reactions.

In this type of reaction energy needed to break the bond are higher than the energy released during bond formation.

For example:

C + H₂O   →  CO  + H₂

ΔH = +131 kj/mol

it can be written as,

C +  H₂O  + 131 kj/mol  →  CO  + H₂

Exothermic reaction:

The type of reactions in which energy is released are called exothermic reactions.

In this type of reaction energy needed to break the bonds are less than the energy released during the bond formation.

For example:

Chemical equation:

C + O₂   →  CO₂

ΔH = -393 Kj/mol

it can be written as,

C + O₂   →  CO₂ + 393 Kj/mol

Answer is

Explanation:

There are mainly four shells in an atom namely K, L, M, and N.

By using 2n², we can find the maximum number of electrons present in M shell.

Let, K = 1st shell, L = 2nd shell, M = 3rd shell, and N = 4th shell.

K = 1, L = 2, M = 3 and N = 4.

K = 2n² = 2(1)² = 2(1) = 2.

L = 2n² = 2(2)² = 2(2) = 4.

M = 2n² = 2(3)² = 2(9) = 18.

N = 2n² = 2(4)² = 2(16) = 32.

So, The maximum number of electrons present in the M shell is