How tough is MBA in financial management for a B.Sc. (Chemistry) Hons. Student?

Nothing is tough, if you have interest in it. If you have interest in management, and want your career in this field then it will be a good approach as you can pursue MBA in spite of being from any other field as MBA first year is all about basics and if you have an interest too, then you can easily

It won't be easy, but the effort you put in would be completely worth it. Management is something you do not learn in any Science related course. So, at first it may seem difficult, but everything is based on basics you learned till class 12th, so brush up on the basics that's it.