Learn Russian: Четверть акций принадлежит акционеру. - A quarter of the shares belongs to the shareholder.

The word четверть (a quarter) is a noun. Just like in English when we say "a quarter of...", Russian uses the Genitive case after fraction nouns to show what the fraction is a part of. Since there are multiple shares, акций is in the Genitive plural.

How is акций formed from its dictionary form?

The dictionary form (Nominative singular) is акция (share/stock). For feminine nouns ending in -ия, the Genitive plural is formed by changing the -я to -ий, giving us акций.

Why is the verb принадлежит singular if we are talking about multiple shares?

In this sentence, the grammatical subject is the singular noun четверть (a quarter), not the shares themselves. Therefore, the verb agrees with четверть and stays in the third-person singular form. If this were in the past tense, it would also take the feminine form (принадлежала) to match четверть.

Why is акционеру in the Dative case?

The verb принадлежать (to belong) requires the Dative case to show who the item belongs to (literally "belongs to the shareholder"). The Nominative form is акционер, and its Dative singular form is акционеру.