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

The area of a square is $5.29\ cm^2$. The area of $7$ such squares taking into account the significant figures is ........... $cm^2$.

$A$ 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:

The mass of a box is $2.3\, kg$. Adding $2.15\, g$ and $12.39\, g$ to it,the total mass is ........ $kg$.

Length,breadth,and thickness of a strip having a uniform cross-section are measured to be $10.5 \ cm$,$0.05 \ mm$,and $6.0 \ \mu m$,respectively. Which of the following option$(s)$ give$(s)$ the volume of the strip in $cm^3$ with correct significant figures?

What is the number of significant figures in the result of $(3.20 + 4.80) \times 10^5$?