На обед бабушка приготовила плов, а к мясу подала пюре.

Because the subject is бабушка, which is grammatically feminine.

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

• masculine: приготовил
• feminine: приготовила
• neuter: приготовило
• plural: приготовили

So:

• бабушка приготовила
• бабушка подала

A male subject would give приготовил and подал instead.

На обед is a very common expression meaning for lunch.

Here, обед is in the accusative case. With на, Russian often uses the accusative when talking about purpose, destination, or something intended for an event/meal/time:

• на завтрак — for breakfast
• на обед — for lunch
• на ужин — for dinner

So На обед бабушка приготовила плов means something like For lunch, grandmother made pilaf.

This is more idiomatic than trying to translate English word-for-word.

Because the sentence describes completed actions.

• приготовила comes from приготовить — to prepare, to cook, to get ready
• подала comes from подать — to serve, to hand, to present

Perfective verbs are used when the speaker sees the action as a whole, with a result:

• she cooked/prepared the pilaf
• she served the mashed potatoes

If you used imperfective verbs such as готовила or подавала, the focus would be more on the process, repetition, or background action rather than the completed result.

А often connects two parts while also showing a slight contrast, shift, or separate piece of information.

Here it is something like:

• she made pilaf for lunch, and/as for the meat, she served mashed potatoes

Using и would sound more like a simple addition of one action to another.
Using а helps separate the two ideas a little:

1. what she made for lunch
2. what she served with the meat

So а is very natural here because it introduces a second, slightly distinct detail.

К мясу uses the preposition к with the dative case:

• nominative: мясо
• dative: мясу

In food-related contexts, к often means to go with, as an accompaniment to, or for something:

• соус к рыбе — sauce for fish / sauce to go with fish
• гарнир к курице — a side dish for chicken
• пюре к мясу — mashed potatoes to go with meat

So к мясу подала пюре means she served mashed potatoes with the meat / as a side for the meat.

Why not с мясом?
Because с мясом usually means together with meat in a more literal sense, as if the two are physically served or combined together. К мясу specifically expresses the idea of an accompaniment or side dish.

Because пюре is an indeclinable noun in Russian.

That means it keeps the same form in all cases:

• пюре
• нет пюре
• к пюре
• вижу пюре
• с пюре
• о пюре

Many borrowed words in Russian are indeclinable, especially some nouns ending in -е, -о, -и, or -у.
So even though пюре is the direct object here, it still stays пюре.

It is in the accusative, but for many masculine inanimate nouns, the accusative looks the same as the nominative.

• nominative: плов
• accusative: плов

Since плов is masculine and inanimate, its accusative singular does not change in form.

Compare:

• Я вижу стол — I see the table
• Я приготовила плов — I cooked pilaf

But with animate masculine nouns, accusative often matches the genitive instead:

• Я вижу брата

So плов is accusative here, even though it looks unchanged.

Because а is joining two clauses, and Russian normally puts a comma before coordinating conjunctions like а in this kind of sentence.

The two parts are:

1. На обед бабушка приготовила плов
2. а к мясу подала пюре

Even though the subject бабушка is not repeated in the second part, it is understood from the first clause. Russian still treats this as a compound structure, so the comma is standard.

Because it is already clear that the same person is doing both actions.

Russian often omits repeated elements when they are easy to understand from context. In English we often do the same:

• Grandma made pilaf for lunch and served mashed potatoes with the meat.

We do not need to repeat Grandma before served. Russian works similarly here.

If you did repeat it, it would usually sound heavier or more emphatic.

Yes, Russian word order is flexible, and the chosen order reflects emphasis and information structure.

This version starts with:

• На обед — setting the context first: for lunch
• then бабушка — who did it
• then приготовила плов — what she made

In the second part:

• к мясу comes early to highlight what the mashed potatoes went with

A different order is possible, for example:

• Бабушка приготовила плов на обед, а пюре подала к мясу.

That also works, but the emphasis shifts slightly. The original sounds natural because it foregrounds the meal context and then the accompaniment relationship.

It is broader than simple restaurant-style served.

The verb подать can mean:

• to serve food
• to hand something over
• to present
• to bring something to the table

In this sentence, к мясу подала пюре suggests that she put mashed potatoes on the table or offered them as the side dish for the meat.

So served is a good translation, but the Russian verb has a wider range of uses depending on context.