Its arbitrary. It was developed on the greek phoenetic system and never reallybwas explained.
Answer:- 10 L of ethane.
Solution:- The given balanced equation is:

From this equation, ethane and oxygen react in 2:7 mol ratio, the ratio of volumes would also be same if they are at same temperature and pressure.
Since 14 L of each gas are taken, the oxygen will be the limiting reactant and ethane will be the excess reactant. Let's calculate the volume of ethane used:

= 
From above calculations, 4 L of ethane are used. So, excess volume of ethane left after the completion of reaction = 14 L - 4 L = 10 L
Hence, 10 L of ethane will be remaining.
Answer:
Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.
Answer:
As you move across a period, the atomic mass increases because the atomic number also increases. ... The atomic mass for any given atom mainly comes from the mass of the protons and neutrons.
Explanation: