Taking into account the significant figures,what is the value of $9.99\, m - 0.0099\, m$ (in $, m$)?

The area of a rectangular field (in $m^{2}$) of length $55.3 \ m$ and breadth $25 \ m$ after rounding off the value for correct significant digits is

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

Time periods of oscillation of the same simple pendulum measured using four different measuring clocks were recorded as $4.62 \,s, 4.632 \,s, 4.6 \,s$ and $4.64 \,s$. The arithmetic mean of these readings in correct significant figures is: (in $\,s$)

Match the number of significant figures in the given column:

Column-$I$	Column-$II$
$(a)$ $0.007\ m^2$	$(p)$ $2$
$(b)$ $2.64 \times 10^{24}\ kg$	$(q)$ $1$
$(c)$ $0.0021\ g\ cm^{-3}$	$(r)$ $4$
$(d)$ $0.0006032\ J$	$(s)$ $3$

What are significant figures? What are significant digits? Explain with examples.