यह एक आम वजह है।

A natural pronunciation is:

• यह — yeh (in careful reading, you may also hear yah)
• एक — ek
• आम — aam (long aa sound)
• वजह — wajah or vajah
• है — hai

So the whole sentence sounds roughly like:

yeh ek aam wajah hai

A few notes:

• यह is often written one way but pronounced more like yeh in everyday speech.
• व in Hindi can sound somewhere between English v and w, so वजह may sound like vajah or wajah depending on the speaker.

In this sentence, यह most directly means this.

So:

• यह = this
• यह एक आम वजह है। = This is a common reason.

But in real Hindi, यह can sometimes also feel like it, depending on context. Hindi uses demonstratives like यह and वह in places where English might use personal pronouns.

For a beginner, the safest understanding here is:

• यह = this

एक literally means one, but it is also often used like a/an in English.

So:

• एक आम वजह = a common reason

Hindi does not have true articles like a/an/the, so एक is often used when you want to express a/an clearly.

Compare:

• यह आम वजह है। = This is a common reason.
• यह एक आम वजह है। = This is a common reason.

Both can work, but एक makes the indefinite sense a bit more explicit.

Yes — आम can mean both mango and common.

This is a very common point of confusion for learners.

Here:

• आम = common / ordinary

But in another sentence:

• आम मीठा है। = The mango is sweet.

How do you know which meaning is intended?
You figure it out from context.

In एक आम वजह, the meaning is clearly a common reason, not a mango reason.

वजह means reason or cause.

Yes, it is generally treated as a feminine noun in Hindi.

For example:

• यह वजह है।
• यह अच्छी वजह है। = This is a good reason.

Notice अच्छी is the feminine form of अच्छा, agreeing with वजह.

In your sentence, आम does not change form for gender here, so you do not see any obvious feminine marking on it.

Hindi sentence structure is different from English.

English says:

• This is a common reason.

Hindi usually puts the verb at or near the end:

• यह एक आम वजह है।

So the pattern is:

• यह = this
• एक आम वजह = a common reason
• है = is

This is very normal in Hindi. The verb है often comes at the end of simple present-tense sentences.

Some Hindi adjectives change depending on the gender and number of the noun, but others do not.

आम is one of the adjectives that usually stays the same.

So you get:

• आम वजह = common reason
• आम बात = common thing / common matter
• आम लोग = common people / ordinary people

By contrast, a changing adjective like अच्छा would behave like this:

• अच्छा कारण
• अच्छी वजह
• अच्छे लोग

So आम is convenient because it does not need to change here.

Yes, you could say:

• यह एक आम कारण है।

That also means This is a common reason/cause.

The difference is mostly in tone and usage:

• वजह is very common in everyday speech.
• कारण can sound a bit more formal or bookish in some contexts.

Both are correct, but वजह often sounds more natural in ordinary conversation.

Yes, यह is singular: this.

The plural is:

• ये = these

So:

• यह एक आम वजह है। = This is a common reason.
• ये आम वजहें हैं। = These are common reasons.

Notice the other changes too:

• वजह → वजहें for plural
• है → हैं for plural

In everyday spoken Hindi, many speakers pronounce यह more like ये, so you may hear something that sounds like:

• ये एक आम वजह है

But in standard written Hindi, for singular this, the usual form is:

• यह

So the best beginner rule is:

• यह = singular this
• ये = plural these

Just be aware that actual speech is often looser than textbook writing.

The pattern is:

यह + एक + adjective + noun + है

Breaking it down:

• यह = this
• एक = a / one
• आम = common
• वजह = reason
• है = is

So this is a very useful template. You can build many similar sentences:

• यह एक अच्छी किताब है। = This is a good book.
• यह एक बड़ा सवाल है। = This is a big question.
• यह एक आम समस्या है। = This is a common problem.

Yes. Just like in English, the adjective comes before the noun:

• आम वजह = common reason

So inside the noun phrase:

• एक comes before the adjective and noun
• आम comes before वजह

That gives:

• एक आम वजह = a common reason

This part is actually quite friendly for English speakers, because the order feels familiar.

You can add नहीं before है:

• यह एक आम वजह नहीं है।

That means:

• This is not a common reason.

A very useful beginner pattern is:

• X है = X is
• X नहीं है = X is not

So:

• यह वजह है। = This is the reason.
• यह वजह नहीं है। = This is not the reason.