zhè shì xǐyījī.

They work like this:

• 这 = the subject, meaning this
• 是 = the linking verb, like is
• 洗衣机 = the noun that identifies what this is, meaning washing machine

So the structure is:

subject + 是 + noun

That is a very common Mandarin pattern for identification.

Mandarin normally does not use articles like a, an, or the.

So 洗衣机 by itself can mean:

• a washing machine
• the washing machine
• washing machine in a general classification sense

The exact meaning depends on context. In 这是洗衣机, the idea is simply This is a washing machine.

In 这是洗衣机, 这 is being used by itself as a pronoun meaning this.

这个 often means this one and can also be used, but it may sound a bit more specific, colloquial, or contrastive depending on context.

Compare:

• 这是洗衣机。 = This is a washing machine.
• 这个是洗衣机。 = This one is a washing machine. / This here is the washing machine.

Also, if 这 goes directly before a noun, you usually need a measure word:

• 这台洗衣机 = this washing machine

So in your sentence, 这 is standing alone, not directly modifying 洗衣机.

Not necessarily.

这是洗衣机 is perfectly normal, especially when you are simply identifying something.

But you can also say:

• 这是一台洗衣机。

Here, 一台 is a number + measure word combination, and 台 is the usual measure word for machines like washing machines, TVs, and computers.

So both are possible:

• 这是洗衣机。
• 这是一台洗衣机。

The version with 一台 is a little more explicit.

是 is a linking verb used to connect one thing with another for identification.

In this sentence, it links:

• 这 = this
• 洗衣机 = washing machine

So it works like is in This is a washing machine.

A useful thing to remember: 是 is mainly used when what comes after it is a noun or noun phrase.

For example:

• 这是老师。 = This is a teacher.
• 他是学生。 = He is a student.

But Chinese usually does not use 是 before plain adjectives:

• 这个很大。 = This is big.
• not normally 这个是大。

The pinyin is:

zhè shì xǐ yī jī

The tones are:

• 这 zhè — 4th tone
• 是 shì — 4th tone
• 洗 xǐ — 3rd tone
• 衣 yī — 1st tone
• 机 jī — 1st tone

A few pronunciation tips:

• zh in zhè is a retroflex sound, not exactly like English j
• sh in shì is also retroflex
• x in xǐ is a soft sound made with the tongue high and lips spread
• j in jī is a Mandarin sound, softer than English j

In natural speech, the 3rd tone in xǐ is often not fully dipped; it may sound like a lower tone before the following 1st tone.

Because 洗衣机 is one vocabulary word, even though it has three characters.

In pinyin, syllables are often grouped by word, not by character. So:

• 洗 = xǐ
• 衣 = yī
• 机 = jī

but together as one word:

• 洗衣机 = xǐyījī

This reflects how Mandarin works: many words are made of two or more characters.

They break down like this:

• 洗 = wash
• 衣 = clothes or clothing
• 机 = machine

So the literal idea is:

wash-clothes-machine

That is exactly how Mandarin builds the word washing machine.

Yes, it is natural.

It is especially common when:

• pointing something out
• labeling an object
• teaching vocabulary
• identifying something clearly

Native speakers might also say:

• 这是一台洗衣机。
• 这是台洗衣机。

Those are also natural. The version with 台 sounds a bit more concrete because it includes the measure word for machines.

Not if you want a complete sentence with the meaning This is a washing machine.

• 这是洗衣机。 = a full sentence
• 这洗衣机 = more like this washing machine, a noun phrase

So without 是, it stops being a full identification sentence and becomes just a phrase.

The simplest way is to add 吗 at the end:

• 这是洗衣机吗？ = Is this a washing machine?

Another very common way is the A-not-A pattern:

• 这是不是洗衣机？

Both are natural.

You negate 是 with 不:

• 这不是洗衣机。

So:

• 是 = is
• 不是 = is not

This is the standard way to negate identification sentences with 是.