What is 2nd largest star?

There's no way to answer that.

Here's why:

There are billions of galaxies full of stars. Estimates of the number of stars in the Milky Way

galaxy alone (that's the galaxy we're in) range up to 400 billion. If we could measure the size

of one star every second, it would take us over 12,000 years to measure the sizes of all the

stars in the Milky Way alone.

The point here is: Nobody has any idea what star is the largest, smallest, hottest, coolest,

heaviest, lightest, oldest, youngest, brightest, dimmest, or where any of them is.