According to ohm’s law, the ratio of voltage to current in a conductor is

a. constant
b. variable

According to Ohm’s law, the ratio of voltage to current in a conductor is  constant.

Option A

Explanation:

Ohm's law defines that an electric current flowing through the conductor between two ends is directly proportionate to the voltage at these two points. The introduction of a constant proportionality, resistance, gives a simple mathematical equation describing this relationship. Particularly, Ohm's law also mentions that R is constant in this respect, i.e. not dependent on the current.

Where,  

I is the current conduction in amperes

V is the voltage calculated by the conductor in volts

R is the conductor’s resistance in ohms.