1.54 x 10^5 mg
The atomic weight of nickel is 58.6934
Since you have 2.63 moles, the mass will be
2.63 * 58.6934 = 154.3636 grams.
Multiply by 1000 to get milligrams
154.3636 * 1000 = 154363.6 g
Convert to scientific notation
1.543636 x 10^5
Look at the available options and see what matches.
3.56 x 10^5 mg ; Nope, way too big
1.54 x 10^5 mg; Matches to the number of significant figures given.
2.23 x 10^4 mg; Nope, way too small
129 mg; Nope, way too small.
