Animisha I am fully with you on this one. However, my confusion is not "is this curved line called a tie or a slur?" My confusion is: "Does this curved line mean that I should hold the same note in the intervals or chords, or does this curved line mean that I should play the intervals or chords legato?"
I think a way to word the answer is:
If that curved line goes from a note to the same note, then you play those "two same notes" as one continuous note. If the curved line goes from a note to a different note, then you play them legato.
I think in one of your questions there were two voicings in a same clef - one with stem-up notes (voice 1), the other with stem-down notes. The stem-up are one singer's music: stem-down are the other singer's music. So if "singer 1" has the same note twice, then it's a tie = the same note continues as if one single note.
Does this clarify or confuse?