The least count of a vernier callipers is:

1. 1 cm
2. 0.001 cm
3. 0.1 cm
4. 0.01 cm

0.01 cm

Reason — Least count of a vernier callipers is given by the formula:

$\text{Least count (L.C.)} = \dfrac{\text{ Value of 1 main scale div (x)}}{\text {total no. of div on vernier(n)}}$

Hence, least count of a vernier callipers whose main scale is graduated to read 1 mm and vernier scale has 10 division will be:

$\text{Least count (L.C.)} = \dfrac{1\text{ mm}}{10} \\[0.5em] \text{Least count (L.C.)} = 0.1\text{ mm} = 0.01\text{ cm} \\[0.5em]$