What are the elements so i can help?????
Answer: The black ball will have more mass than the white ball.
Explanation: Density of a substance is defined as the ratio of mass and volume occupied by the substance.
Mathematically,

We are given that the two balls are of same size, which means that the volume of both the balls are same. We are also given that the black ball is more dense than the white ball, which means that the black ball will have more mass.
As, 
Unit Cell is the basic <span>repeating structural unit of a crystalline solid .</span>
0.1 km
2cm/year * 5000 yrs = 10000 cm
1cm= .01 m
1km = 1000 m
so the answer is 0.1 km
so you can see those fluorine atoms have really spread out around the central phosphorus atom. this gives us a trigonal bi-pyramidal molecular geometry for pf5.