Answer: 0.5 mm
Explanation: The smallest division that a common ruler has is 1 mm so any measurement taken is approximately accurate to a mm.
Uncertainty of any measuring instrument is the inaccuracy or lost of precision that occur due to its less divisions in an instrument
Uncertainty= Least Count /2
Uncertainty= 1 mm /2
Uncertainty= 0.5 mm
it means that measurement can be 2.3cm ± 0.5mm