zhè shì yànzhèngmǎ.

In 这是验证码。, 这 is being used as a pronoun, so it means this by itself.

• 这 = this
• 是 = is
• 验证码 = verification code

So the structure is:

• 这 + 是 + 验证码
• This + is + a verification code

This is different from using 这 directly before a noun, like:

• 这个验证码 = this verification code

In that case, 这 is not standing alone; it is modifying a noun.

是 is the verb to be in sentences where one thing is being identified as another.

In 这是验证码。, 是 links 这 and 验证码, just like is in English:

• 这 是 验证码。
• This is a verification code.

A very common beginner pattern is:

• A 是 B
• A is B

Examples:

• 这是老师。 = This is a teacher.
• 那是我的手机。 = That is my phone.

Mandarin usually does not use articles like a, an, and the the way English does.

So 验证码 can mean:

• a verification code
• the verification code

The exact meaning depends on context.

In this sentence, English naturally uses a:
This is a verification code.

But Chinese does not need a separate word for that here.

Because 这 is not directly modifying a noun in this sentence.

Compare these two patterns:

1. 这 是 验证码。
   Here, 这 means this by itself. No measure word is needed.

2. 这 个 验证码
   Here, 这 directly modifies 验证码, so a measure word is needed:

   • 这 = this
   • 个 = measure word
   • 验证码 = verification code

So:

• 这是验证码。 = This is a verification code.
• 这个验证码 = this verification code

That is a very important difference.

In modern Mandarin, 验证码 is normally treated as one word meaning verification code.

It can be understood in parts:

• 验证 = to verify / verification
• 码 = code

Together:

• 验证码 = verification code

Even though Chinese characters each have their own meaning, learners should usually memorize 验证码 as a single vocabulary item.

The pinyin is yànzhèngmǎ.

Tone by tone:

• 验 = yàn (4th tone)
• 证 = zhèng (4th tone)
• 码 = mǎ (3rd tone)

So the full sentence is:

• 这 zhè — 4th tone
• 是 shì — 4th tone
• 验证码 yànzhèngmǎ — 4th, 4th, 3rd tones

A rough pronunciation guide:

• zhè sounds somewhat like juh with a falling tone
• shì sounds somewhat like shir with a falling tone
• yàn sounds like yen with a falling tone
• zhèng sounds like jung with a falling tone
• mǎ sounds like ma with a dipping 3rd tone

No. Standard written Chinese normally does not put spaces between words.

So the normal written form is:

• 这是验证码。

The spaced version:

• 这 是 验证码。

is just a learner-friendly way to show the parts more clearly.

Yes, you can, but it feels slightly different.

• 这是验证码。 = This is a verification code.
• 这个是验证码。 = This one is a verification code. / This is a verification code.

这个 often sounds a little more specific or a little more spoken, depending on context.

In many situations, 这是验证码。 is the simpler and more standard choice.

Yes.

• 这 = this
• 那 = that

So:

• 这是验证码。 = This is a verification code.
• 那是验证码。 = That is a verification code.

This is a very common substitution pattern in beginner Chinese.

A simple way is to add 吗 at the end:

• 这是验证码吗？
• Is this a verification code?

This is a basic yes/no question pattern:

• statement + 吗

So:

• 这是验证码。 = This is a verification code.
• 这是验证码吗？ = Is this a verification code?