Answer:
C
Step-by-step explanation:
A rational number can be expressed in the form
[tex]\frac{a}{b}[/tex] ← a, b are integers
A
[tex]\sqrt{81}[/tex] = 9 = [tex]\frac{9}{1}[/tex] ← rational
B
9.5 = 9 [tex]\frac{1}{2}[/tex] = [tex]\frac{19}{2}[/tex] ← rational
C
π is irrational then 5π is irrational
D
[tex]\sqrt{3^2}[/tex] = [tex]\sqrt{9}[/tex] = 3 = [tex]\frac{3}{1}[/tex] ← rational
