An element's atomic number is 45. how many protons would an atom of this element have?

It would have 45 protons, as the atomic number is equivalent to the amount of protons

Name: Rhodium 
Symbol: Rh 
Atomic Number: 45 
Atomic Mass: 102.9055 amu 
Melting Point: 1966.0 °C (2239.15 K, 3570.8 °F) 
Boiling Point: 3727.0 °C (4000.15 K, 6740.6 °F) 
Number of Protons/Electrons: 45 
Number of Neutrons: 58 
Classification: Transition Metal 
Crystal Structure: Cubic 
Density @ 293 K: 12.41 g/cm3 
Color: silverish