Three.
8
It is: 12.66 cm
The zero is not counted in the significant digits. It only indicates the accuracy. To count significant don't count zeroes unless it between other non-zeroes.
0.00185
Three.
8
Two of them.
1.004 cm
It is: 12.66 cm
It is 307 cm.
Yes.
38 cm
(152 cm/(2.54 cm/in)/(12.0 in/ft) = 4.99 feet, to the justified number of significant digits.
Two - all nonzero numbers are significant.
The zero is not counted in the significant digits. It only indicates the accuracy. To count significant don't count zeroes unless it between other non-zeroes.
Two, the number of significant digits in the least precisely stated datum, 2.5 cm.