Which of the following statements is correct?

An ammeter has a range of $1 \ A$ without a shunt. The range of the ammeter can be changed by using different shunt resistances. What is the nature of the graph between the shunt resistance and the range?

$A$ galvanometer with $30$ divisions has a current sensitivity of $20 \, \mu A/division$. Its resistance is $25 \, \Omega$. How will you convert it into an ammeter to measure $1 \, A$ current?

Which one of the following modifications may increase the sensitivity of a moving coil galvanometer?
$1^{st}$ Way: By using a spring of smaller torsion constant.
$2^{nd}$ Way: By using a smaller coil.
$3^{rd}$ Way: By using a stronger magnet.
$4^{th}$ Way: By using a coil having fewer number of turns.

$STATEMENT-1$: The sensitivity of a moving coil galvanometer is increased by placing a suitable magnetic material as a core inside the coil.
$STATEMENT-2$: Soft iron has a high magnetic permeability and cannot be easily magnetized or demagnetized.

$A$ microammeter has a resistance of $100\,\Omega$ and a full-scale range of $50\,\mu A$. It can be used as a voltmeter or as a higher-range ammeter provided a resistance is added to it. Pick the correct range and resistance combination.