You are talking about part of a cake, so the noun ‘cake’ is uncountable. Nouns that are usually uncountable are used as countable nouns when we talk about different types or varieties. ‘Cheese’ is usually uncountable. In this sentence we are talking about the different varieties of cheese, so it is countable.

Many nouns can have both mass noun and countable noun forms, depending on how they are expressed. For example, coffee is a mass noun in the phrase “some coffee” but a countable noun in the phrase “a coffee”.

Some nouns can be thought of as either countable or mass nouns. For example, you could offer someone ‘a chocolate’ (countable) or ‘some chocolate’ (mass).

Most uncountable nouns relate to:

• liquids (milk, water)
• abstract ideas (advice, chaos, motivation)
• powder and grain (rice, wheat, sand)
• mass nouns (furniture, hair, transportation)
• natural phenomena (sunshine, snow, rain, weather)
• states of being (sleep, stress, childhood)

chocolate ​Definitions and Synonyms ​‌‌

1 juice /ˈʤuːs/ noun. plural juices. 1 juice. /ˈʤuːs/ plural juices.

The noun soap can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be soap. However, in more specific contexts, the plural form can also be soaps e.g. in reference to various types of soaps or a collection of soaps.

The plural form of bus is buses. To be fair, a few dictionaries do list busses as an alternative plural form of bus. The buses start running early in the morning.

Until 1961, ‘busses’ was the preferred plural of ‘bus’ in Merriam-Webster dictionaries. But the word ‘buss’ is a synonym of ‘kiss’.