A rational number is an algebraic term expressed as a fraction. The fraction can also be in decimals but only if the decimal places are not repeating or not infinitely long. If they aren't, then these are called irrational numbers.
Let's try each of the choices:
A. The term 2/4 is a rational number. Now, when 0.3 or 3/10 is added to it, the sum would be 4/5 or 0.8. This is a rational number.
B. √7 is an irrational number because its exact value is 2.645751311.... Even if you add 0.3 to it, the answer would still be irrational
C. Obviously, this is an irrational number
D. The exact value of π is 3.14159...... If 0.3 is added to it, the answer would be 3.441592654. This is irrational.
Therefore, the answer is A.