Three - zeros between significant digits are significant.
2 significant figures.
Three.
3 three
20.009 has five significant digits. The g isn't a digit and probably stands for grams.
There is 1 significant figure in this measurement.
Two
Three - all nonzero digits are significant.
Three - all nonzero digits are significant.
50.4 has three significant digits.
It is 13.2 g.
100(23.9/30.3) = 78.9 % Ni, to the justified number of significant digits. 100(6.4/30.3) = 21 % O, to the justified number of significant digits. Fewer significant digits are given for the oxygen percentage because one of its input data, 6.4, has only two significant digits.