The online round consisted of five sections - aptitude, technical, logical reasoning, verbal ability, and coding. Each section was timed. The MCQ section had easy/moderate questions (you can find them at indiabix.com). In the coding section, there were two questions to be solved in 60 minutes. One was on simple string encryption. The other one was based on graphs and was moderately difficult. Solving one of the coding questions and a decent score in other sections was enough to get shortlisted.

It was completely based on my CV. I was asked in-depth about my summer project and the details of the tech stack I used. One of my projects was a spell-checker using the Linked List data structure. I was asked how will it be done on a larger scale (he gave an example of Google). I suggested a Hashing Based approach on which he agreed that it will be faster but asked me to optimize the space requirement, which I was unable to answer.

It started with my introduction. Then there were typical HR questions like -
Why should we hire you?
How did you come to know about Citi?
How will you handle the situation of a dispute with your manager?

Research about the company before the interview and also listen to the Pre-placement talk carefully. It will come in handy.

Be thorough with your resume, don't write anything that you won't be able to justify. For HR, you can prepare the generally asked questions beforehand (do not rote learn, have a mental map of which points to include). Read about the STAR method to answer behavioral questions.
Keep practicing and stay confident it's not that difficult :)
All the best.