C. is the answer. i know because i had this question not that long ago.
Answer:
The initial volume of Ne gas is 261mL
Explanation:
This question can be answered using Ideal Gas Equation;
However, the following are the given parameters
Initial Pressure = 654mmHg
Finial Pressure = 345mmHg
Final Volume = 495mL
Required
Initial Volume?
The question says that Temperature is constant;
This implies that, we'll make use of Boyle's law ideal gas equation which states;
Where 
represent the initial pressure
represent the final pressure
represent the initial temperature
represent the final temperature
Substitute these values in the formula above;
Divide both sides by 654
(Approximated)
<em>The initial volume of Ne gas is 261mL</em>
Which of these what?
This isn't clear, can you put the answer choice or something?
<span>Chemists considered Martian
Periodic Table as one of the most useful tools they’ve used whose purpose is to
arrange the Martian elements according
to their properties and their atomic number. On this periodic table, it was
found out that the properties seem to vary.
Dmitri Mendeleev, the first to arrange the periodic table according to
atomic mass in a manner that the elements with the same properties were grouped
together. It was Henry Moseley who later arranged the periodic table in accord
to the increasing number of atoms per element. </span>
