A box contains a mixture of small copper spheres and small lead spheres. The total volume of both metals is measured by the displacement of water to be 423 cm^3 and the total mass is 4.35 kg. What percentage of the spheres are copper?

44.01% of the spheres are copper

Explanation:

mass Cu + mass Pb = 4.35kg =  4.35 x 1000 = 4350g

But

Volume= mass / density

Let the volume of copper be C  

density of  Cu = 8.94 g/cm^3

Mass of copper = 8.94C

Let the volume of Lead be L  

density of  lead = 11.34g/cm^3

Mass of lead  = 11.34L

Since  

mass Cu + mass Pb = 4350kg

therefore

8.94C + 11.34L = 4350g EQN A

also

volume of copper + volume of lead =  423 cm^3

Volume of Lead ,L=423-C

putting the value of C = 423-L in Equation A becomes

8.94C + 11.34L = 4350g

8.94C + 11.34(423-C)= 4350g

8.94C+ 4796.82-11.34C=4350

4796.82-4350=11.34C- 8.94

446.82=2.4C

C= 186.175

Volume of copper = 186.175cm^3

Percentage copper = volume copper / total volume metal x 100/1

= 186.175 cm^3 / 423 cm^3 x 100/1

= 44.01%

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explanation:

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since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.