Answer: (3) silicon
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Silicon (Si)
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: ethane 
, propanone 
and water 
Theoretical yield is the quantity of a product obtained from the complete conversion of the limiting reactant in a chemical reaction. It is the amount of product resulting from a perfect chemical reaction and thus not the same as the amount you'll actually get from a reaction.
The answer is four hundred
Explanation: Process is diffusion. The gas molecules follow a zig-zag path through the tube as they collide with the air molecules in the tube. The purpose of the glass tube is to eliminate air currents and to see if the gas molecules will move on their own.
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