Ka for CH3COOH is 1.8×10-5 and Kb for NH4OH is 1.8×10-5. The pH of ammonium acetate will be

(1) 7.005

(2) 4.75

(3) 7.0

(4) Between 6 and 7

Hint: pH=7+pKa-pKb2
Given that, 
Ka for CH3COOH=1.8×10-5Kb for NH4OH=1.8×10-5
Ammonium acetate is a salt of a weak acid and weak acid. For such salts
pH=7+pKa-pKb2=7+[-log 1.8×10-5]-[-log 1.8×10-5]2=7+4.74-4.742=7.00