Answer:
2
Step-by-step explanation:
4.0 has 2 significant digits.
The zeros after a non zero number are significant.
Any non zero number is significant.
0.004 has 1 significant digit.
4000 has 4 significant digits.
In your case 4.0 × 10^3 there is an exception because it is in scientific notation. So there are 2 significant digits.
hope this makes sense.
:)
