Die Banane liegt schon auf dem Tisch, aber die Birne bleibt in meiner Tasche.

Both Banane and Birne are feminine nouns in German. The definite article for feminine nouns in the nominative singular is die.

In this sentence, both nouns are the subjects of their clauses:

• Die Banane liegt ...
• die Birne bleibt ...

So die is the correct form in both places.

German often uses different verbs depending on the position of something.

• liegen = to lie, to be lying, to be in a horizontal position
• stehen = to stand, to be standing
• sitzen = to sit, to be sitting

A banana is thought of as something lying on a surface, so Die Banane liegt auf dem Tisch sounds natural.

English often just uses is, but German prefers these more specific location verbs.

Because this sentence describes a location, not movement.

The preposition auf is a two-way preposition. That means it can take:

• dative for location: on the table
• accusative for movement toward a destination: onto the table

Here the banana is already there, so we use the dative:

• auf dem Tisch = on the table

Compare:

• Die Banane liegt auf dem Tisch. = The banana is on the table.
• Ich lege die Banane auf den Tisch. = I put the banana onto the table.

Because Tisch is a masculine noun: der Tisch.

After auf in a location meaning, German uses the dative case. The masculine dative singular article changes like this:

• der → dem

So:

• der Tisch = the table
• auf dem Tisch = on the table

For the same reason as auf dem Tisch: this clause describes where the pear stays, not movement into the bag.

in is also a two-way preposition:

• dative for location: in meiner Tasche = in my bag
• accusative for movement into something: in meine Tasche = into my bag

Here the pear remains inside the bag, so German uses the dative:

• in meiner Tasche

Compare:

• Die Birne bleibt in meiner Tasche. = The pear stays in my bag.
• Ich stecke die Birne in meine Tasche. = I put the pear into my bag.

Because Tasche is feminine (die Tasche), and after in with a location meaning, the noun phrase is in the dative.

The possessive mein- changes its ending depending on case, gender, and number.

For feminine singular:

• nominative: meine Tasche
• accusative: meine Tasche
• dative: meiner Tasche

So:

• in meiner Tasche = in my bag

bleiben means to remain or to stay. It suggests that something continues to be in a place.

So:

• Die Birne ist in meiner Tasche. = The pear is in my bag.
• Die Birne bleibt in meiner Tasche. = The pear stays/remains in my bag.

Using bleibt creates a contrast with the first clause: the banana is already on the table, but the pear is still staying in the bag.

Yes. bleiben is not only for people. It can also be used for things when you mean they remain where they are.

Examples:

• Das Buch bleibt auf dem Regal.
• Der Schlüssel bleibt in der Schublade.
• Die Birne bleibt in meiner Tasche.

It simply means the object is not being moved.

Here schon means already.

• Die Banane liegt schon auf dem Tisch = The banana is already on the table.

It suggests that this situation is already true now, perhaps earlier than expected, or in contrast with the pear still being elsewhere.

Be careful: schon can mean different things in different contexts, but already is the right meaning here.

German main clauses usually follow the V2 rule: the finite verb is in the second position.

First clause:

• Die Banane | liegt | schon auf dem Tisch

Second clause:

• die Birne | bleibt | in meiner Tasche

Even though the second clause comes after aber, it is still a normal main clause, so the verb stays in second position.

Because aber is a coordinating conjunction. Coordinating conjunctions connect two main clauses and do not push the verb to the end.

So you get:

• ..., aber die Birne bleibt in meiner Tasche.

Compare that with a subordinating conjunction like weil, which does move the verb:

• ..., weil die Birne in meiner Tasche bleibt.

So aber behaves more like English but.

Because German normally uses a comma to separate two main clauses joined by conjunctions like aber.

So:

• Die Banane liegt schon auf dem Tisch, aber die Birne bleibt in meiner Tasche.

This is standard German punctuation.

Yes, grammatically you can say Die Banane ist auf dem Tisch, and it would be understood.

But liegt is usually more natural and idiomatic, because German often chooses a verb that describes the object’s physical position.

So:

• ist auf dem Tisch = correct, but more general
• liegt auf dem Tisch = more natural for an object resting on a surface

Because in German, all nouns are capitalized.

So:

• die Banane
• der Tisch
• die Birne
• die Tasche

This is a basic spelling rule in German and applies whether the noun is common or proper.