Answer is : (a) 0.1 mm
Here, 10 divisions of vernier scall = 11 main scale divisions
So, 1 vernier scale division = 11/10 main scale divisions
Now, we use formula for least count, Least count = 1 main scale division − 1 vernier scale division.
![](https://www.sarthaks.com/?qa=blob&qa_blobid=3972967080227977809)
So, magnitude of least count is 0.1 mm.