What is the difference between reaction rate and rate constant?

Kindly go through the solution 

$K=A.e^{-Ea/RT}=\left(6.5\times 10^2\right)e^{-26000K/T}$

$\frac{Ea}{8.314}=26000$

Ea = 216.164kJ/mol $\cong$ $$ 216

Yes, in elementary reactions, order and molecularity can be the same, but this is not always the case because order is an experimental quantity, and molecularity is a theoretical concept.

Reaction Kinetics, also known as chemical kinetics, is the study of the rate of chemical reaction and the factors affecting the reaction rate, such as temperature, concentration, and catalyst.

A → 2B
t = 0: 1 mole 0
after 100 min: (1 - 0.1) mol 0.2 mol
K = (1/t)ln [a/ (a-n)]
K = (2.303/100)log (1/0.9) min? ¹
0.693/t? /? = (2.303/100) [log10 - log9] = (2.303/100) x 0.046
t? /? = 69.3 / (2.303 x 0.046) = 654.15 min
Ans. = 654 (the nearest integer)