Answer : The number of marbles lined up across the circumference of the earth can be,
marbles
Explanation :
First we have to calculate the diameter of tiny marble.

r = radius of marble = 0.25 mm

Now we have to calculate the number of marbles can be lined up across the circumference of the earth.
Given:
Circumference of the earth distance =

conversion used:

Number of marbles can be lined up =
marbles
Thus, the number of marbles lined up across the circumference of the earth can be,
marbles