To determine the order of magnitude of a number N , we express it as N = n × 10x If 0 .5 < n ≤ 5 , then x will be the order of magnitude of N. The given value 9.82 x 1018 can be expressed as 0 .982 x 1019 As, 0 5 < 0.982 < 5. the order of magnitude is 19. Hence, option 'C' is correct