The number of significant figures in $200.40$ is

Which of the following measurements is the most accurate?

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?

The decimal equivalent of $\frac{1}{20}$ up to three significant figures is

The area of a sheet of length $10.2 \,cm$ and width $6.8 \,cm$ expressed up to the proper number of significant figures is ......... $cm^2$.

The result after adding $3.8 \times 10^{-6}$ and $4.2 \times 10^{-5}$ with due regard to significant figures is: