Calculate the mass difference between two iron substances, weighing 6.39852 g and 6.39 g, respectively.

Perform the following operation. Express the answer using the correct number of significant figures.

[(2.9 x 10³) ÷ (1.78 x 10⁴)] + 4.97

How many significant figures does each arithmetic calculation have?

(i) (456.32 + 891.23) (ii) (8.00 x 12.67 ) / 2.392 (iii) [ ( 28.12 x 9.0 ) + 12.56 ]