Lewis diagram:
well first you have to know the Valence electrons the elements which will on top of the periodic table.
for examples:
H2O
it will be O-H-O and the dots will on top. oxygen have 6 valence electrons so that mean it need 6 dots. also for H it will have 7 V-electrons.
Answer : The reagent present in excess and remains unreacted is, 
Solution : Given,
Moles of 
= 3.00 mole
Moles of = 2.00 mole
Excess reagent : It is defined as the reactants not completely used up in the reaction.
Limiting reagent : It is defined as the reactants completely used up in the reaction.
Now we have to calculate the limiting and excess reagent.
The balanced chemical reaction is,
From the balanced reaction we conclude that
As, 2 moles of react with 1 mole of
So, 3.00 moles of react with 
moles of
From this we conclude that, is an excess reagent because the given moles are greater than the required moles and is a limiting reagent and it limits the formation of product.
Hence, the reagent present in excess and remains unreacted is,
Answer:
I) Change in solubility
II) Change in boiling point
III) Change in colour
Explanation:
A chemical change involves formation of new products and is not reversible.
So, once two liquid solutions are mixed and a chemical change takes place, the new product will have the following:
- a new solubility rate, i.e it will dissolve at a rate different from the two liquid solution
- a new boiling point i.e it takes a new point at which its molecules liberate to yield vapour
- a new colour might be detected, as the individual solution each has its own colour
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