The uncertain digit in the measurement of a length reported as $41.68 \,cm$ is ...........

Time periods of oscillation of the same simple pendulum measured using four different measuring clocks were recorded as $4.62 \,s, 4.632 \,s, 4.6 \,s$ and $4.64 \,s$. The arithmetic mean of these readings in correct significant figures is: (in $\,s$)

The volume of a sphere is $1.76 \ cm^3$. The volume of $25$ such spheres in terms of significant figures is ...... $cm^3$.

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

What is a significant number? What is a significant digit?

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