The radius of a circle is $2.12 \ m$. Its area according to the rule of significant figures is ......... $m^2$.

An object of mass $m = 3.513 \ kg$ moves along the $x$-axis with a velocity of $5.00 \ ms^{-1}$. The magnitude of its momentum can be recorded as $...... \ kg \ ms^{-1}$.

$A$ student measuring the diameter of a pencil of circular cross-section with the help of a vernier scale records the following four readings: $5.50\, mm, 5.55\, mm, 5.45\, mm, 5.65\, mm$. The average of these four readings is $5.5375\, mm$ and the standard deviation of the data is $0.07395\, mm$. The average diameter of the pencil should therefore be recorded as:

Match List-$I$ with List-$II$.

List-$I$ (Number)	List-$II$ (Significant figures)
$A. 1001$	$I. 3$
$B. 010.1$	$II. 4$
$C. 100.100$	$III. 5$
$D. 0.0010010$	$IV. 6$

Choose the correct answer from the options given below:

The number of significant figures in $4.870 \ m$ is

"Changing the units of measurement does not change the number of significant figures." Explain with an example.