Answer:
- The last digit, 8, is the uncertain one.
Step-by-step explanation:
Every measurement has an uncertainty associated with the instrument used to measure.
The measurement represented by 5.678 grams has 4 significant digits: all the non-zero digits in a measurement are significant (non-zero digits and zeros between non-zero digits are always significant).
When you use a scale to measure the mass of an object, such scale has an appreciation and the last number that you can read is between two possible numbers, i.e. the digit 8 in the given measurement could have been a little bigger or a little smaller, so the real measurement could have been something between 5.677 . . . or 5.678 . . .
The last digit in any measurement is always uncertain.