One.
10 significant figures.
I think you meant how many significant figures are in 10? The answer is one.
Three.
Rounded to one significant figure it becomes 10
It's already there.
To 1 significant figure, it would be 8 x 10^3.
It has 1 significant figure.
10
10
10
0.004 has 1 significant figure.
0.3 has one significant figure.