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

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

If the value of resistance is $10.845 \, \Omega$ and the value of current is $3.23 \, \text{A}$,the value of potential with significant figures would be ........... $V$.

The addition of three masses $1.6 \,g$,$7.32 \,g$,and $4.238 \,g$,expressed to the proper number of decimal places,is ....... $g$.

The radius of a thin wire is $0.16 \; mm$. The area of cross-section taking significant figures into consideration in square millimeters is?

The number of significant figures in $6.25 \times 10^5$ is