Answer : The value of
for the final reaction is, 
Explanation :
The following equilibrium reactions are :
(1)

(2)

(3)

The final equilibrium reaction is :

Now we have to calculate the value of
for the final reaction.
First half the equation 1, 2 and 3 that means we are taking square root of equilibrium constant and then add all the equation 1, 2 and 3 that means we are multiplying all the equilibrium constant, we get the final equilibrium reaction and the expression of final equilibrium constant is:

Now put all the given values in this expression, we get :


Therefore, the value of
for the final reaction is, 
Answer:
NH4+(aq) → NH3(aq) + H+(aq)
Explanation:
Following arrhenius, an acid can be defined as:
An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in water.
NH4+(aq) → NH3(aq) + H+(aq)
The ammonium ion acts as a weak acid in aqueous solution, dissociating into ammonia and a hydrogen ion.
An Arrhenius base is a substance that, when added to water, increases the concentration of OH- ions in water.
NH4+(aq) will not dissciate in OH- ions. So it's not a base, but an acid.
1) C
2) B
3) A/B not sure
4) C I think