Three classes: 28×3=84 students
8 test tubes per student: 84× 8= 672
hope this helps!
Answer: Compound
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: Copper 
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: water 

Thus as it give that the red sample on being heated, a gas is released and a blue powder is left after the heating. Thus the given sample is a compound.
Different types of acid deposition are
sulphur dioxide
nitroges oxides
Answer:
5 L
Explanation:
Use Charles law and rearrange formula
Change C to K
- Hope that helped! Please let me know if you need further explanation.