Answer:

-) Oxidizing agent: 
-) Reducing agent: 
Explanation:
The first step is separate the reaction into the <u>semireactions</u>:
A.
B.
If we want to balance in <u>basic medium </u>we have to follow the rules:
1. We adjust the oxygen with 
2. We adjust the H with 
3. We adjust the charge with 
Lets balance the first semireaction A. :

Now, lets balance semireaction B:

Finally, we have to add the two semireactions:
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Cancel out the species on both sides:

Simplifying the equation :

The
is <u>oxidized</u> therefefore is the <u>reducing agent</u>. The
is<u> reduced</u> therefore is the <u>oxidizing agent</u>.
Electrons = protons
protons = atomic number
protons + neutrons = atomic mass
Therefore: a) protons + 7 = 15
protons= 15 -7
protons= 8
B) Remember proton = atomic number
so atomic number = 8
C)Now we know the atomic number so we can easily check on the periodic table what element has an atomic number of 8, which is Oxygen
Explanation:
water near where a river enters the ocean is having a higher density.
coz, ocean water has salt which increases water's density