A sentence is a statement if it can be said to be true or false, not both, without any ambiguity.
True
This is the definition of the mathematical statement. The sentence shouldn't be of the form of a request, order, question etc. for which we can't decide if its true or false.
Usually we represent statement by small alphabets.
Example: p:5>2
q: √2 is a rational number
r: New Delhi is the capital of India