On May 31, 2020, the Corporation gave Bob Jones, a member of the board of directors who also has provided consulting services to the Corporation from time to time, an incentive stock option to purchase 50,000 shares of its common stock at an exercise price of $0.10 a share. The option vested over a four-year period, with equal amounts exercisable on each monthly anniversary date of the grant after a six-month cliff (that is 6/48th vested after six months). On April 30, 2021, the fair market value of the Corporation's common stock was $0.30 per share and Bob decided to exercise his option with respect to all shares that had vested. How many shares could Bob purchase on April 30, 2021, pursuant to the May 31, 2020 grant? Did Bob have any tax liability at the time of exercise? Why or why not?