Answer
(a) Soluble
(b) Soluble
(c) Insoluble
(d) Insoluble
Work Step by Step
(a) Almost all compounds with the amonnium cation are soluble.
(b) A lot of sulfate salts are soluble, and a Zinc one is not an exception.
(c) Most sulfide salts are insoluble, and the nickel one is not an exception.
(d) Most sulfate salts are soluble, but according to the figure 3.10, $BaSO_4$ is an exception.