Answer
a. It is a weak acid.
b. It is a strong acid.
c. It is a strong acid.
d. It is a weak acid.
Work Step by Step
a. When $HCHO_{2}$ is dissolved in water it partially ionizes. Hence it is a weak acid.
b. When $H_{2}SO_{4}$ is dissolved in water it completely ionizes. Hence it is a strong acid.
c. When $HNO_{3}$ is dissolved in water it completely ionizes. Hence it is a strong acid.
d. When $H_{2}CO_{3}$ is dissolved in water it partially ionizes. Hence it is a weak acid.