Answer:
 Correct option is:
B. square root 65 units
Explanation:
Pythagorean theorem states that the square of hypotenuse is equal to the sum of squares of the legs of the right angled triangle.
Here, we are given that:
The legs of a right triangle are 4 units and 7 units.
By Pythagoras theorem
Hypotenuse²=4² +7²
 = 16+49
 = 65
⇒ Hypotenuse= 

Hence, Correct option is:
B. square root 65 units