Yes, a compound is a type of matter.
Answer:- density of the liquid is 0.21 gram per mL.
Solution:- 
From given data, mass of cylinder = 10.4 g
mass of cylinder along with liquid = 11.7 g
So, mass of liquid = 11.7 g - 10.4 g = 1.3 g
Volume of liquid = 6.2 mL
Let's divide the mass by the volume to get the density of the liquid:

density = 
So, the density of the liquid is 0.21 gram per mL.
B directly; inversely
Pressure and volume have an inverse relationship (when one increases the other increases) while volume and temperature are direct (if one increases so does the other)
Note: these relationships are only true if other factors are constant such as the temperature, and amount (in moles).
The question is incomplete.
The complete question probably is
The pH scale for acidity is defined by pH = − log₁₀[H⁺] where [H⁺] is the concentration of hydrogen ions measured in moles per liter (M). A solution has a pH of 2.55. Find the hydrogen ion concentration.
Answer: -
0.003 M
Explanation: -
pH = − log₁₀[H⁺]
Thus the hydrogen ion concentration [H⁺] = 
= 
= 0.003 M