What does variable resistor means?

Which of the units given below is the SI unit of resistance?

Observe the correlation in the first pair and complete the second pair:
$1 \mathrm{volt}=\frac{1 \mathrm{Joule}}{1 \mathrm{Coulomb}}$:: $1 \mathrm{ohm}=$________

The diagram below shows a dual control switch circuit connected to a bulb. Copy the diagram and complete it so that the bulb is switched ON.

Three resistances $x_1,x_2,x_3$ are connected in a circuit in different ways. $x$ is the effective resistance. The properties observed for these different ways of connecting $x_1,x_2,x_3$ are given below. Write the way in which they are connected in each case. (I-current, V-potential difference, x-effective resistance)

 Current I flow through $x_1,x_2,x_3$.

The voltage-current ($V$-$I$) graph of a metallic conductor at two different temperature $T_1$ and $T_2$ is shown in figure. At which temperature is the resistance higher?

When two resistors are connected in series, their effective resistance is $80 \Omega$. When they are connected in parallel, their effective resistance is $20 \Omega$. What are the values of the two resistances?

Resistances $R_1,R_2,R_3$ and $R_4$ are connected as shown in the figure. $S_1$ and $S_2$  are two keys. Discuss the current flowing in the circuit in the following cases.

Both $S_1,S_2$ are closed.

The resistance of a $1 \mathrm{m}$  long Nichrome wire is $6 \Omega$. If we reduce the length of the wire to $70 \mathrm{cm}$. What will its resistance be?