Remember, OIL RIG
Oxygen Is Loss of electrons
Reduction Is Gain of electrons
If something goes from + to - then it has gained electrons
If something goes from neutral to - it has gained electrons
If it goes from - to + is loses electrons
If it goes from neutral to + it loses electrons
If something is oxidised, it is a reducing agent
If something is reduced, it is an oxidising agent
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Answer:
HClO4(aq) + H2O(l) ⇄ H3O+(aq) + ClO4-(aq)
Explanation:
When an acid dissolves in water, it will produce hydronium ion, H3O+ as the only positive ion.
perchloric acid, HClO4, being an acid will react with water, H2O to produce hydronium ion, H3O+ as shown below:
HClO4(aq) + H2O(l) ⇄ H3O+(aq) + ClO4-(aq)
Answer:
The mass of liquid comes out to be 82 g.
Explanation:
Given density of liquid = 1.64 g/mL
Given volume of liquid = 50 mL
The relation between density and volume is shown below

Mass of liquid = 
Mass of 50 mL liquid = 82 g