The correct answer is (a) 510 k
The best I can explain: We can store 510 k characters in sessionStorage in chrome 23.0, for chrome 18.0 and chrome 24.0 we can store unlimited characters, for chrome 19.77 its value is 1021 k, for chrome 25.0 and 27.0 it is 2.49 M, for chrome 28.0, 30.0, 31.0, 31.1 its value is 4.98 M.