Assuming that voltage remains constant, as its diameter decreases, its current decreases. hence option D is correct.
What is Current ?
Current is a flow of charges. it is denoted by i and expressed in ampere A. Mathematically it is expressed as i = q/t, where q is the amount of charge and t is time. Current is nothing but amount of charges flown in the unit time in the electric wire. Charge is expressed in coulomb C and time in second s. hence coulomb per second (C/s) is ampere A. Charge on electron is 1.60217663 × 10⁻¹⁹C which is called as elementary charge.
There are two types of the current, Convectional current and non-conventional current. Convectional current is the current flows from positive to negative. Non convectional current flows from negative to positive. Note that flow of electrons is from negative to positive. Hence direction of flow of conventional current is from positive to negative.
In this problem, voltage is constant and diameter of the wire is decreasing,
The relation between resistance and and resistivity is
R = ρ l/A
When diameter decreases, cross sectionals area decreases, it increases resistance of the wire. and due to increase in resistance, current decreases in order to keep the voltage constant(V=IR).
Hence option D is correct.