Йогурт полезнее сладкой газировки.

Полезнее is the comparative form of полезный (healthy, beneficial, good for you).

So:

• полезный = healthy / beneficial
• полезнее = healthier / more beneficial

In this sentence, it means that yogurt is being compared with sweet soda, and yogurt is the healthier one.

A very literal breakdown is:

• Йогурт = yogurt
• полезнее = is healthier
• сладкой газировки = than sweet soda

After a comparative like полезнее, Russian often uses the thing being compared in the genitive case instead of using a separate word for than.

So Russian commonly says:

• Йогурт полезнее сладкой газировки.

Literally, this is closer to:

• Yogurt is healthier than sweet soda

But grammatically, Russian is using:

• comparative + genitive

This is a very common pattern.

Because Russian has two common ways to make this kind of comparison:

1. Comparative + genitive

   • Йогурт полезнее сладкой газировки.

2. Comparative + чем

   • Йогурт полезнее, чем сладкая газировка.

Both mean the same thing: Yogurt is healthier than sweet soda.

The version without чем is often more compact and very natural.

Because сладкой has to agree with газировки, which is in the genitive singular.

The noun is:

• газировка = sweet soda / soft drink / fizzy drink

Its genitive singular is:

• газировки

Since газировка is feminine singular, the adjective сладкий must match it:

• nominative: сладкая газировка
• genitive: сладкой газировки

So сладкой is simply the correct feminine genitive singular form.

Йогурт is in the nominative case.

It is the item being described as healthier, so it stays in its basic dictionary form here.

You can think of the structure like this:

• Йогурт = the thing being talked about
• полезнее = is healthier
• сладкой газировки = than sweet soda

So the first item stays nominative, while the second item often goes into the genitive after the comparative.

Yes, you could, but it sounds less natural in a simple everyday sentence.

Russian often prefers the short comparative form:

• полезнее

rather than:

• более полезный

So:

• Йогурт полезнее сладкой газировки.
• Йогурт полезнее, чем сладкая газировка.

are more natural than:

• Йогурт более полезный, чем сладкая газировка.

The более + adjective pattern is possible, but it is often used in more formal, analytical, or stylistically heavier language.

Yes. Полезней is an alternative comparative form of полезный.

So both are possible:

• полезнее
• полезней

In many contexts, полезнее sounds more neutral and standard, while полезней can sound a little more conversational or stylistically lighter.

For a learner, полезнее is the safest form to use first.

Газировка is a casual, everyday word for a carbonated soft drink or soda.

With сладкой, the phrase means something like:

• sweet soda
• sugary soft drink
• sweet fizzy drink

So the point of the sentence is that yogurt is healthier than a sugary soda.

Yes, Russian word order is fairly flexible, but the given version is the most neutral:

• Йогурт полезнее сладкой газировки.

You could also hear other orders for emphasis, such as:

• Сладкой газировки йогурт полезнее.

This still means the same thing, but it sounds more marked or contrastive, as if emphasizing compared with sweet soda.

For learners, it is best to use the neutral order first.

The stress is:

• ЙОгурт
• полЕзнее
• слАдкой
• газирОвки

So the sentence is pronounced approximately like:

• ЙОгурт полЕзнее слАдкой газирОвки

If you are practicing aloud, the most important thing is to keep the stress in the right place, because Russian vowel pronunciation depends heavily on stress.

Yes. In the present tense, Russian normally does not use a word for is / are in sentences like this.

English says:

• Yogurt is healthier than sweet soda.

Russian says:

• Йогурт полезнее сладкой газировки.

There is no present-tense to be here, and that is completely normal.