Which of the following acts as a circuit protection device?

The internal resistances of two cells shown in the figure are $0.1\,\Omega$ and $0.3\,\Omega$. If $R = 0.2\,\Omega$,find the potential difference across the cells.

An electric bulb of $60 \, W, 120 \, V$ is to be connected to a $220 \, V$ source. What resistance should be connected in series with the bulb so that the bulb glows properly?

$A$ cell whose e.m.f. is $2\, V$ and internal resistance is $0.1\,\Omega$ is connected with a resistance of $3.9\,\Omega$. The voltage across the cell terminal will be ................ $V$.

$A$ parallel combination of two resistors,of $1 \,\Omega$ each,is connected in series with a $1.5 \,\Omega$ resistor. The total combination is connected across a $10 \,V$ battery. The current flowing in the circuit is .............. $A$

The current flowing in a coil of resistance $90 \,\Omega$ is to be reduced by $90\%$. What value of resistance should be connected in parallel with it? ............. $\Omega$