Which class. includes snail, slug, and limpets.
(a)Cephalopoda
(b)Scaphopoda
(c)Gastropoda
(d)Amphineura

Hint: It is a taxonomic class within the phylum Mollusca which is the largest group under this phylum that includes snails and slugs of all kinds and all sizes and they show an anatomical process called torsion where during development the visceral mass of the animal rotates 180° to one side such that the anus is situated more or less above the head.

Complete answer:
This class Gastropoda contains over 35,000 living and 15,000 fossil gastropod species that comprise the largest class under the phylum and which includes the limpets, top shells, periwinkles, slipper shells, snails, slugs, sea hares, abalones, nudibranchs, or sea slugs, and sea butterflies. The organisms under the class Gastropods are primarily marine, but freshwater and terrestrial forms occur. The typical gastropod shell is a three-layered when presented, its spiral whorl is made up of calcium carbonate which varies in color, shape, ornamentation, and size according to the species and within this shell, there is a tall, coiled body mass but some forms such as slugs are shell-less and do not have a tall body mass. Again this organisms’ larvae undergo a twisting, or torsion, that brings the rear of the body (mantle cavity, gills, and anus) to a position near the head and results in the twisting of internal organ systems. In adults this twisted form is seen to be retained; but in others, it is partially lost.

Additional Information: 1) Three subclasses are seen under this class Gastropoda: the Prosobranchia that contains the majority of gastropods; the Pulmonata that contains the land snails; and the Opisthobranchia, which includes the sea hares and sea slugs.
2) Later subclass under the class Gastropoda is seen to consist of animals that have reduced shells or none at all, among them most gastropods are motile, but some are sedentary like the slipper shell ( Crepidula ).
3) The process of reproduction in this class is variable but most gastropods have separate sexes also the fertilization of the eggs occurs in seawater. Here some gastropods are hermaphrodites (having both sexes in the same individual) in nature while some are protandric hermaphrodites, i.e., they are male first and become female as they age.
4)Gastropods were described by Georges Cuvier in the scientific literature in 1795 which derives from the Ancient Greek word refers to the fact that the animal's "foot" is positioned below its guts.
So, the correct answer is, ‘Gastropoda’.

Note: The class Gastropods are seen to be economically valuable as food for many animals, including humans, but some of the gastropods are serious pests; e.g: the common slug causes much garden damage.