На столе лежали заколка, серёжки и тонкий браслет, которые она собиралась надеть вечером.

Because на столе means on the table in the sense of location.

After на, Russian usually uses:

• Prepositional case for location: на столе = on the table
• Accusative case for movement toward a place: на стол = onto the table

So:

• На столе лежали... = the items were already there
• Она положила заколку на стол = she put the hair clip onto the table

Because the real subject is the whole list:

заколка, серёжки и тонкий браслет

Together, these make a plural compound subject, so the verb is plural: лежали.

Even though the first noun is singular, the sentence is talking about several items lying on the table.

This word order is very natural in Russian. It has a scene-setting feel:

На столе лежали... = On the table lay...

Russian often puts the location first and then introduces the things that are there. It sounds descriptive and flows well in narrative.

You could also say:

Заколка, серёжки и тонкий браслет лежали на столе.

That is also correct, but it sounds a bit more neutral and puts more focus on the objects themselves rather than the setting.

Лежали is more specific and vivid than были.

• были would just mean were
• лежали means were lying

Since these are small objects on a table, Russian naturally uses лежать. It gives a physical picture of how they were positioned.

So:

• На столе были... = more neutral, just states existence
• На столе лежали... = more concrete and natural here

They are in the nominative case, because they are the subject of лежали.

Forms here:

• заколка — nominative singular
• серёжки — nominative plural
• тонкий браслет — nominative singular

Even though two of them are singular individually, together they form a plural subject.

Because earrings are very often spoken of as a pair.

Russian has a singular form серёжка meaning an earring, but when someone is talking about the jewelry they plan to wear, серёжки usually means earrings as a pair.

So the sentence likely means:

• one hair clip
• a pair of earrings
• one thin bracelet

Because the adjective тонкий modifies only браслет.

Russian does not automatically make an adjective apply to all items in a list unless the grammar clearly connects it to all of them. Here the structure is:

• заколка
• серёжки
• тонкий браслет

So only the bracelet is described as thin/delicate.

If the speaker wanted one adjective for all the items, the sentence would need a different structure.

Because которые она собиралась надеть вечером is a relative clause.

In Russian, relative clauses are normally separated by commas:

• ..., которые...
• ..., который...
• ..., которая...

So the comma marks the start of extra information about the objects.

Because которые refers to the whole group of items, not to just one noun.

The antecedent is:

заколка, серёжки и тонкий браслет

That is a plural group, so the relative pronoun must also be plural:

• singular masculine: который
• singular feminine: которая
• plural: которые

So которые means which/that referring to all three items together.

Excellent question. Here которые is actually accusative plural, because it is the direct object of надеть.

She was going to put on what?
→ которые = those items

Why does it look like nominative? Because for inanimate plural nouns and pronouns, nominative plural and accusative plural have the same form.

So in this sentence:

• grammatical role inside the relative clause: direct object
• case: accusative plural
• form: которые

If the antecedent were animate, you would often see a different form, such as которых.

Because собиралась + infinitive usually points to an intended action, and here the action is viewed as a single completed act: putting the items on for the evening.

• надеть = perfective
• надевать = imperfective

Собиралась надеть means she was planning/intending to put them on.

If you used собиралась надевать, it would sound less natural here unless you wanted to stress a repeated/process-like idea. For getting dressed with specific accessories for one occasion, надеть is the normal choice.

This is a very common learner question.

Standard Russian distinguishes them like this:

• надеть = to put on an item
• одеть = to dress a person

So:

• надеть браслет = to put on a bracelet
• одеть ребёнка = to dress a child

Since she is putting on jewelry, надеть is correct.

A common memory aid is:

Надеть что-то, одеть кого-то.

Because Russian often uses the instrumental case by itself for parts of the day used as time expressions.

So:

• утром = in the morning
• днём = in the daytime / during the day
• вечером = in the evening
• ночью = at night

Here вечером means in the evening or that evening.

Because Russian past tense agrees with the subject in gender and number.

The subject here is она, so the verb is feminine singular:

• он собирался
• она собиралась
• оно собиралось
• они собирались

So она собиралась надеть... means she was going to put on...

In this sentence, the normal reading is that it refers to all three items.

That is because:

1. the pronoun is plural: которые
2. semantically, it makes sense that she planned to wear all the accessories listed

If the writer wanted the clause to refer only to браслет, they would use singular masculine:

..., тонкий браслет, который она собиралась надеть вечером.

But as written, которые clearly points to the entire list.