Explanation:
It is given that, the diameter of the sun is, d = 1.391 million kilometers
We need to represent the diameter in scientific numbers. A number can be written in scientific form as :

Where
p is any real number
q is any integer
Since,

and 1 km = 1000 m
The diameter of sun is:


So, the diameter of the sun is
. Hence, this is the required solution.