<u>Answer:</u> The density of the quartz is 2.68 g/mL
<u>Explanation:</u>
We are given:
Volume of graduated cylinder = 50.3 mL
Volume of quartz + graduated cylinder = 64.8 mL
Volume of quartz = [64.8 - 50.3] mL = 14.5 mL
To calculate the density of substance, we use the equation:

Mass of quartz = 38.9 g
Volume of quartz = 14.5 mL
Putting values in above equation, we get:

Hence, the density of the quartz is 2.68 g/mL
Answer:
CH4 + 2 O2 → CO2 + 2 H2O
Explanation:
There are one mole of O2 on the left side and on the right side there are three moles of O2. And to fix it you would need to make it two moles of O2 to have four molecules of O2 on the left side. Then you would make two moles of H2O to have a total of four moles of O2 on the right. Therefore, CH4 + 2 O2 → CO2 + 2 H2O is the answer.
Answer: 58.44g
Explanation: The molar mass of NaCl is 58.44g.