Which of the following is a base SI unit?

The side of a square is measured as 10 cm with an absolute error of 0.1 cm. The percentage error in its area is approximately:

If $Z = A^2 B / C$, the maximum relative error in $Z$ is:

The percentage error in a measured quantity $a$ (with absolute error $\Delta a$) is:

Using rules of significant figures, the product $2.5 \times 1.25$ should be reported as:

The number of significant figures in $1.050 \times 10^3$ is: