W1 is the best way to make shape.
Then if later B“a” with atari, W“b” traps that stone and makes the needed second eye.
W“c” instead of W1 seems superficially equivalent, but although it’s exactly the same as the correct W1 insofar as assuring the life of the White group is concerned, the correct W1 has the potential followup of W“d”, while W“c” has no such followup potential because after the White group becomes safe the 6 Blacks to their left are just unequivocally dead!