Hi Navneeth,
Yes, as *ig said, it's a baritone at the beginning. It's a long phrase, but not really impossible. The tenor solo comes later in the piece, and his phrases are pretty simple.
The toughest for me? Hmmm....
I could say it's whatever I'm working on at the moment....
In retrospect, I'd like to think it wasn't so tough, but at the time, my first principle role as Benny Southstreet in an abbreviated production of
Guys and Dolls was among the biggest of challenges for me. I had been invited to be a chorister for the show, and in the first cast readthrough, all of the production people looked at me and thought I'd make a good Benny(who was actually a melding of the Benny and Nicely Nicely characters). I had no idea if I could come up with a New York accent, let alone
act. It was a lot of work and a lot of stress, but was greatly rewarding. I used to have a very blurry video tape of the show, and I came across very well, if I say so myself.
Another huge challenge for me was my first season as tenor soloist/section leader for Jewish High Holidays. My only exposure to Hebrew up to that time was one performance of the Chichester Psalm, so I was a total neophyte. I had a two inch binder of music to learn in five rehearsals, so I ended up doing a lot of homework, and I was very insecure about my ability to rise to the occasion.
Now, I practically have the whole book memorized....
Last instance: One of my early goals when I started singing again after getting out of the Navy was to join the San Diego Master Chorale, at that time under the direction of Frank Almond. I auditioned on Dec 28th. The neophyte strikes again: I sang a solo, was stopped halfway through("I've heard enough."), and did some sightreading. Afterward, Frank commented that it sounded like I'd done some "solo work," which usually connotes being a professional soloist in front of an orchestra. I had no idea, and thinking about having sung solos in church, etc., I told him sure, I'd done solo work.

He then asked if I'd done Beethoven's 9th before. I'd not only not done it, I wasn't sure how it went! I told him I hadn't, and he told me the Master Chorale would be performing it on Jan 14th, and he'd like it if I could join them for that performance. So, I learned the choral movement of the 9th in two weeks. I was also only one of two new members asked to do it. The other guy knew the piece.
Funny you should bring up the 9th....
A slight hijack here...
Under the heading of "most exhilarating", it would have to be my first production with the SDO. We did
Turandot which has become my favorite opera. It was a hugely lavish production with phenomenal principle singers. At the end of the opening night performance, I was bawling while we sang the final chorus.