Explanation

(a)
g equivalent of $\left( NH_{4} \right)_{2}SO_{4} = \frac{100}{1000} \times \frac{1}{10} \times 66 = 0.66$
g equivalent of$Na_{2}CO_{3} \bullet H_{2}O = \frac{0.62}{62} = 0.01$
left $\left( NH_{4} \right)_{2}SO_{4}$ is $0.66 - 0.01 = 0.65$
$\left( NH_{4} \right)_{2}SO_{4}$ is a salt of strong acid and weak base