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

$A$ person measures the mass of $3$ different particles as $435.42 \ g$,$226.3 \ g$,and $0.125 \ g$. According to the rules for arithmetic operations with significant figures,the sum of the masses of the $3$ particles will be: (in $g$)

What is the number of significant digits for a number that does not represent a measurement?

If $L = 2.331 \ cm$ and $B = 2.1 \ cm$,then $L + B =$ (in $cm$)

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

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?