It should be an Electrical conductor, since conductors allow for movement of electrons from one point to another.
So we want to know what is the age of igneous rock if it contains one half of its original amount of potassium 40. The half-life of potassium 40 is 1.251*10^9 years. Since in the igneous rock there is one half of potassium left it means only one half-life has passed. And its age is 1.251*10^9 years or 1.251 billion years.
Answer:
Resistance, 

Given:
V = 407.1 V
Current through the resistor, I = 0.850 mA = 
Time constant for the circuit,
Solution:
Initially the capacitor is uncharged, the current in the circuit remains same.
Thus
At t = 0
the current in the circuit, I = 
Therefore,
Resistance, R = 
R = 
Now, for calculation of Capacitance, C:
Time constant for the circuit, 

