Democritus developed the atomic model. He theorized that atoms were specific to the material which they composed. He also believed that the atoms different in size and shape, were in constant motion in a void, collided with each other; and during these collisions, could stick together.
It's called a compound because different elements are held together by a chemical bond.
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
Secretary of State John Hay sent his Open Door Notes (1899-1900) to world powers to protect United States trading interests in China. The correct option among all the options that are given in the question is option "3". These notes were mainly in regards to providing equal opportunity for trades in China and also respecting China's sovereignty, territorial integrity and administration. The principles of operating in China was the same for the British as well as for the United States, but John Hay was the first person to give it a written form. After this the official policy of the United States was based on the written document during the first half of the 20th century.
The average molecular weight of the mixture can be calculated using this formula:
MWav = x1MW1 + x2MW2
Where x is the mass fraction of the components of the mixture, in this case, copper (63.546 g/mol) and zinc (<span>65.38 g/mol).
</span>
x1 = 7.36 / (7.36+0.51)=0.935
x2 = 0.51 / (7.36+0.51)=0.065
So,
MWav = 0.935(63.546) + 0.065(65.38) = 63.665 g/mol
