After two half lives, the fraction of nuclei remaining is : (a) 1/2 (b) 1/9 (c) 1/8 (d) 1/4

D

Explanation:

After each half life, half the original amount remains.

So after two half lives, (1/2)^2 remains, or 1/4.

  distance on the y-axis and time on the x-axis.

explanation:

the instantaneous velocity = change in position/time taken

the slope of the graph should give instantaneous velocity.

  slope of a graph = change in value of y -axis / change in values of x -axis

  comparing both the equations

    change in value of y -axis = change in position

  change in values of x -axis = time taken

so position values should be on the y axis and time values should be on the x axis.

distance on the y-axis and time on the x-axis.