The sum of probabilities of all the outcomes experiment is less than 1.(true/false)

Dear student,

The sum of the probabilities of all the outcomes must equal 1. Hence it is false.
 

For example,
A coin has two possible outcomes : Heads or Tails.
Probability of Heads = $\frac{1}{2}$
Probability of Tails = $\frac{1}{2}$
The sum of probabilities of all the outcomes = $\frac{1}{2}$ + $\frac{1}{2}$ = 1

Regards