Этот кекс оказался мягче, чем вчерашний пирог.

Оказался is the past tense of оказаться, which often means to turn out to be or to prove to be.

So:

• Этот кекс был мягче... = This cake was softer...
• Этот кекс оказался мягче... = This cake turned out to be softer...

Using оказался adds the idea of a result, discovery, or something that became clear afterward. It often suggests mild surprise or a conclusion based on experience.

Because the subject is кекс, and кекс is a masculine singular noun.

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

• masculine: оказался
• feminine: оказалась
• neuter: оказалось
• plural: оказались

So:

• Этот кекс оказался...
• but Эта булочка оказалась...

Мягче is the normal comparative form of мягкий (soft).

Russian often prefers these short comparative forms:

• мягкий → мягче
• большой → больше
• интересный → интереснее

So мягче means softer.

You can sometimes use более + adjective, but it is usually more formal or less natural here:

• natural: кекс оказался мягче
• less natural in this sentence: кекс оказался более мягким

For simple comparisons like this, мягче is the standard choice.

Because Russian comparative forms like мягче are invariable. They do not agree with the noun the way normal adjectives do.

Compare:

• мягкий кекс
• мягкая булочка
• мягкое тесто

But in the comparative:

• кекс мягче
• булочка мягче
• тесто мягче

The form мягче stays the same.

Чем means than after a comparative.

So:

• мягче, чем вчерашний пирог = softer than yesterday’s pie

This is one of the most common comparison patterns in Russian:

• лучше, чем... = better than...
• быстрее, чем... = faster than...
• интереснее, чем... = more interesting than...

Because Russian uses the adjective вчерашний to mean yesterday’s.

So:

• вчера = yesterday
• вчерашний = yesterday’s / from yesterday

In English, yesterday’s pie uses a possessive-like structure. Russian usually expresses that idea with the adjective вчерашний.

Examples:

• вчерашняя газета = yesterday’s newspaper
• вчерашний суп = yesterday’s soup

So вчерашний пирог means the pie from yesterday.

It is in the nominative case.

After a comparative with чем, the noun is normally left in the same basic form:

• мягче, чем вчерашний пирог
• быстрее, чем поезд
• интереснее, чем книга

So пирог is not a direct object here. It is just the thing being compared to the cake.

Also, вчерашний agrees with пирог:

• masculine singular nominative: вчерашний пирог

They are different kinds of baked goods.

• кекс usually means something like a loaf cake, tea cake, or sometimes a muffin/cupcake-type cake, depending on context
• пирог usually means a pie or a baked dish with some kind of filling

So the sentence is comparing two different baked items: this cake/muffin and yesterday’s pie.

The exact English translation of кекс can vary depending on the food being described.

Этот means this and agrees with кекс.

Because кекс is masculine singular, the correct form is:

• masculine: этот
• feminine: эта
• neuter: это
• plural: эти

So:

• этот кекс = this cake
• эта булочка = this bun/pastry

Yes, but the meaning would change slightly.

• Этот кекс мягче, чем вчерашний пирог.
  = This cake is softer than yesterday’s pie.

This is a straightforward statement.

• Этот кекс оказался мягче, чем вчерашний пирог.
  = This cake turned out to be softer than yesterday’s pie.

This suggests that someone discovered this after trying it, comparing it, or expecting something else.

So оказался adds the idea of an observed result.

Yes, in standard Russian spelling, a comma is normally used before чем in comparisons like this:

• мягче, чем вчерашний пирог
• лучше, чем я думал
• больше, чем нужно

So the comma in your sentence is correct.

Yes. Russian word order is flexible, though some versions sound more natural than others.

The given sentence is neutral and natural:

• Этот кекс оказался мягче, чем вчерашний пирог.

You could also say:

• Этот кекс мягче, чем вчерашний пирог, оказался.

But that sounds marked or stylistically unusual.

For learners, it is best to keep the original order unless you have a reason to emphasize something specific.