Розовый зефир оказался мягче, чем белый.

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

So Розовый зефир оказался мягче... is not just a plain statement of quality. It suggests that, after checking or noticing, the pink marshmallow turned out to be softer.

This verb often adds a small idea of discovery, result, or mild surprise.

Because зефир 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

Since the subject is зефир, the verb must be оказался.

Зефир is a Russian sweet that is often translated as marshmallow, but it is not exactly the same as the typical American marshmallow.

It is usually softer, fruit-based, and more like a whipped confection. In learner materials, marshmallow is a convenient translation, but culturally the Russian dessert is its own thing.

Grammatically, the important point here is that зефир is a masculine noun.

Because мягче is the comparative form of мягкий.

• мягкий = soft
• мягче = softer

The sentence is making a comparison, so Russian uses the comparative form, just like English uses softer instead of soft.

This short comparative form is very common in Russian:

• быстрый → быстрее = faster
• громкий → громче = louder
• мягкий → мягче = softer

Чем means than in comparisons.

The pattern is:

X + comparative + чем + Y

So here:

• розовый зефир = the pink marshmallow
• оказался мягче = turned out softer
• чем белый = than the white one

This is the standard Russian way to compare two things.

Because Russian often leaves out a repeated noun when it is obvious from context.

So чем белый really means:

чем белый зефир

But repeating зефир would sound unnecessary here.

English does something similar with the white one. Russian often just uses the adjective by itself when the noun is understood.

Because белый stands for белый зефир, and зефир is masculine singular.

The adjective must match the hidden noun in gender, number, and case.

So:

• белый = masculine
• белая = feminine
• белое = neuter

Since the omitted noun is зефир, the correct form is белый.

Because after чем in a standard comparison, Russian normally uses the compared word in the nominative form.

So:

• мягче, чем белый = softer than the white one

Here белый is nominative masculine singular.

You may later encounter comparative constructions without чем that use a different case, but in this sentence, with чем, белый is the expected form.

Yes, grammatically you could say более мягкий, which also means softer / more soft, but мягче is the more natural and common choice here.

Compare:

• розовый зефир оказался мягче = natural, concise
• розовый зефир оказался более мягким = also possible, but less simple

Notice that if you use более мягкий after оказался, it would usually change to the instrumental form:

• оказался мягче
• оказался более мягким

So the structure would not stay exactly the same.

Russian often does not use a direct equivalent of was the way English does in simple descriptive sentences. Instead, it uses other structures.

Here, Russian uses оказался to express turned out to be. That is more natural than trying to build the sentence around a past form of to be.

So rather than literally saying The pink marshmallow was softer than the white one, Russian says something closer to The pink marshmallow turned out softer than the white one.

It is in the nominative singular, because it is the subject of the sentence.

• розовый agrees with зефир
• both are masculine singular nominative

That is why you see:

• розовый зефир not
• розового зефира or other case forms

The sentence starts with the thing being talked about, and that thing is the subject.