How many significant figures are there in this expression 0.001050

4 sig fig in that expression

1.all non zero digit are significant
2.zero b/w non-zero digits are significant
3.if number is less than 1 zero on right of decimal point but to the  left of first non-zero digit are not significant

here 4 significant figures are there in 0.001050
123 -3 significant figures
123000-3 significant figures
2.107 - 4 significant figures
0.5610 - 4 significant figures