Which of the following reactions are not feasible?

In the reactivity (activity) series, metals are ranked in decreasing order of chemical reactivity, tracked by their standard electrode potential E°: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, mercury, silver, gold — from most negative E° (most reactive) to most positive (least reactive). A displacement reaction of the form (free metal) + (metal sulfate) → (new sulfate) + (displaced metal) is the standard convention this item is built on: it proceeds only when the free metal's E° is more negative than that of the metal already combined in the sulfate — a less reactive metal cannot displace a more reactive one.

Checking each of the four pairings by standard electrode potential (E°, approximate values vs. SHE):

Cross-check against the full series order: calcium's E° (−2.87 V) is far more negative than zinc's (−0.76 V) — calcium, an alkaline-earth metal, sits near the very top of the series, well ahead of the transition metal zinc. The zinc + calcium sulfate pairing is the only one of the four where the free metal's E° is less negative than the salt-metal's E° — every other pairing has the free metal's E° more negative.

Hence the reaction between zinc and calcium sulfate does not take place; zinc's electrode potential is not negative enough to displace the far more reactive calcium.