(a)
The equivalent circuit model of the carbon resistor can be draw as below,
Here we can know that,
, , ,
The lead capacitor can be calculated,
Assume there will be skin effect in the copper leads, the lead inductance can be given,
The can be indicate as below,
(b)
With 
（c）
With 
(d)
I put two figures into one, and I found that when the frequency increase, the overall impedance closing to one value around 0.6GHz. This is because for large value R, the effect of parasitic capacitance dominates, however for small value R, the effect of parasitic inductance dominates.