A gas can move around freely while a solid is hard and can’t move around freely
The wavelength is the distance between one crest/trough to another crest/trough. On the image, it's basically the length between each peak of the wave. You can see that the distance between peaks in wave A are much shorter than the distance between the peaks in wave B.
Thus, wave B has the longer wavelength.
The question is incomplete, here is a complete question.
An arctic weather balloon is filled with 27.8 L of helium gas inside a prep shed. The temperature inside the shed is 13 ⁰C. The balloon is then taken outside, where the temperature is -9 ⁰C. Calculate the new volume of the balloon. You may assume the pressure on the balloon stays constant at exactly 1 atm. Be sure your answer has the correct number of significant digits.
Answer : The new volume of the balloon is 25.7 L
Explanation :
Charles's Law : It is defined as the volume of the gas is directly proportional to the temperature of the gas at constant pressure and number of moles.

or,

where,
= initial volume of gas = 27.8 L
= final volume of gas = ?
= initial temperature of gas = 
= final temperature of gas = 
Now put all the given values in the above equation, we get:


Therefore, the new volume of the balloon is 25.7 L
The oxidation is occurring on Calcium ions as it release one electron and reduction will be occurring on fluorine ion as it accepts one electron.
<u>Explanation:</u>
An element will undergo oxidation and form a positive ion on releasing one or more electrons from its valence shell. While reduction is occurred in a chemical reaction, then the element will be forming a negative ion with the acceptance of one or more electrons in its valence shell.
So in the given process of calcium fluoride, the one electron from the valence shell of calcium will be released making it as
ions and this is termed as oxidation process. This one electron will be getting accepted by the fluorine ion and thus it will convert to
ions. This process of acceptance of electrons is termed as reduction.
The chemical formula for the compound magnesium perchlorate is Mg(ClO₄)₂
Magnesium perchlorate or Mg(ClO₄)₂ is an ionic compound.
Perchlorate here is an anion which is represented by ClO₄⁻. Perchlorate is a polyatiomic anion, where one Cl atom is bonded to four O atoms.
The magnesium cation is represented by Mg²⁺
So one Mg²⁺ cation combines with two ClO₄⁻ anion to form one molecule of Mg(ClO₄)₂