If the speed of 5 molecules is 1 km per second, 2 km per second, 3 km per second, 4 km per second, 5 km per second, then the root mean square method will be:

(a) 2.24 km per second
(b) 2.82 km per second
(c) 3.16 km per second
(d) 3.54 km per second