What is the number of significant figures in $3400$?

An object of mass $4.237 \, g$ occupies a volume of $1.72 \, cm^3$. The density of the object to appropriate significant figures is ......... $g \, cm^{-3}$.

$A$ body of mass $m = 3.513\ kg$ is moving along the $x$-axis with a speed of $5.00\ ms^{-1}$. The magnitude of its momentum is recorded as ........ $kg\ m/s$.

The radius of the Earth is $6371 \ km$ and the radius of its orbit around the Sun is $149 \times 10^6 \ km$. The order of magnitude of the diameter of the orbit is greater than that of the Earth by

The respective number of significant figures for the numbers $23.023$,$0.0003$,and $2.1 \times 10^3$ are:

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