На полке лежал пончик с глазурью, но я выбрала маленькое пирожное.

На полке means on the shelf.

Here на is being used to show location, so полка goes into the prepositional case:

• полка = shelf
• на полке = on the shelf

Compare:

• на полку = onto the shelf, to the shelf motion/direction
• на полке = on the shelf location

So in this sentence, the doughnut is already there, which is why на полке is correct.

Russian often prefers a more specific verb than English does.

• лежал = was lying
• был = was

For physical objects, Russian commonly uses verbs like:

• лежать = to lie
• стоять = to stand
• висеть = to hang
• сидеть = to sit

A doughnut on a shelf is imagined as lying, so лежал sounds natural.

English might simply say There was a doughnut on the shelf, but Russian often says more literally A doughnut was lying on the shelf.

Because пончик is the subject of лежал.

The basic structure is:

• пончик лежал = the doughnut was lying

Since пончик is the thing doing the action of lying, it stays in the nominative singular.

Here с means with, and after с in this meaning, Russian normally uses the instrumental case.

So:

• глазурь = icing, glaze
• с глазурью = with icing

The form глазурью is the instrumental singular of глазурь.

This noun is feminine and ends in -ь, so its instrumental singular ends in -ью:

• глазурь
• глазурью

In the past tense, Russian verbs agree with the subject in gender and number.

So:

• я выбрал = I chose said by a male speaker
• я выбрала = I chose said by a female speaker

Since the sentence has выбрала, the speaker is female.

This is very common in Russian past tense:

• он выбрал = he chose
• она выбрала = she chose
• оно выбрало = it chose
• они выбрали = they chose

Because пирожное is a neuter singular noun, and the adjective must agree with it.

So:

• маленький = masculine form
• маленькая = feminine form
• маленькое = neuter form

Since пирожное is neuter, the correct form is:

• маленькое пирожное = a small pastry / little cake

Russian adjectives must agree with the noun in:

• gender
• number
• case

Good question. Пирожное is the direct object, so it is in the accusative case. But for neuter inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: пирожное
• accusative: пирожное

The same is true for the adjective here:

• nominative neuter singular: маленькое
• accusative neuter singular inanimate: маленькое

So even though the phrase is grammatically accusative, it looks identical to the dictionary form.

Но means but.

It connects two contrasting ideas:

• На полке лежал пончик с глазурью = There was a doughnut with icing on the shelf
• но я выбрала маленькое пирожное = but I chose a small pastry

So the contrast is: the doughnut was available, but the speaker chose something else.

Yes, the word order can be changed, but the original order sounds natural and neutral.

Original:

• На полке лежал пончик с глазурью, но я выбрала маленькое пирожное.

This presents the setting first:

• On the shelf,
• then what was there,
• then what the speaker chose instead.

You could change the order for emphasis, for example:

• Пончик с глазурью лежал на полке, но я выбрала маленькое пирожное.

This still means the same thing, but it emphasizes пончик с глазурью a bit more directly.

Russian word order is more flexible than English because case endings show grammatical roles, but word order still affects style, emphasis, and information flow.

No, пирожное is not pie.

• пирожное usually means a small pastry, little cake, or individual dessert pastry
• пирог is pie or a large baked pastry
• пирожок is a small stuffed bun/pie

So маленькое пирожное suggests a small sweet pastry or cake-like dessert, not a slice of pie.

Выбрала is perfective.

• выбирать = imperfective, to be choosing / to choose repeatedly
• выбрать = perfective, to choose, to make a choice

In the past tense:

• я выбирала = I was choosing / I used to choose
• я выбрала = I chose, I made the choice

Here the speaker completed the action and selected one item, so the perfective form выбрала is the natural choice.