Which of the following resistivity ( $\rho$ ) $\mathrm{v} / \mathrm{s}$ temperature ( T ) curves is most suitable to be used in wire bound standard resistors?

Sliding contact of a potentiometer is in the middle of the potentiometer wire having resistance $R_p=1 \Omega$ as shown in the figure. An external resistance of $R_e=2 \Omega$ is connected via the sliding contact. The electric current in the circuit is :

The effective resistance between $$A$$ and $$B$$, if resistance of each resistor is $$R$$, will be :

A galvanometer has a coil of resistance $$200 \Omega$$ with a full scale deflection at $$20 \mu \mathrm{A}$$. The value of resistance to be added to use it as an ammeter of range $$(0-20) \mathrm{mA}$$ is :