Answer:
Explanation:
If the deviation is 1.3 g the true measurement will be within the interval 122.4g - 1.3g to 122.4g + 1.3g:
Hence, only the first two digits, hundreds and tens places, are certain. The ones digit is uncertain.
Since, the signficant figures include the certain digits plus one uncertain digit, you should report the number with three significant figures: 2 certain digits + 1 uncertain digit.
The most probable mass of the object would be the mean which is 122.4, which must be rounded to three significant figures, i.e 122 g.