Question

How many significant digits are in 705.0 ?

Answer 1

all trailing zeros after dec. pt are sig.
all nonzero numbers are sig.
all zeros between nonzero numbers are sig.

there are 4 significant digits

Answer 2

There are four significant digits.

Any numbers that's not 0 counts as a significant digit. Since the zeroes in this number are either between two numbers or behind a decimal point, they also count as significant.