सुबह मैं हिंदी लिख रही हूँ।

सुबह is a time word meaning in the morning / morning. In Hindi, time expressions often come near the beginning of the sentence, but the word order is fairly flexible.

So these can all be natural, depending on emphasis:

• सुबह मैं हिंदी लिख रही हूँ।
• मैं सुबह हिंदी लिख रही हूँ।

Putting सुबह first gives a natural time-topic feeling: As for the morning / In the morning, I am writing Hindi.

Because this sentence is in the present progressive: am writing.

In Hindi, with present progressive forms like:

• मैं लिख रहा/रही हूँ = I am writing

the subject stays in the direct form:

• मैं

You use मैंने mainly with many perfective past transitive verbs, for example:

• मैंने पत्र लिखा। = I wrote a letter.

So here, मैं is correct because the sentence is not a perfective past sentence.

Because लिख रही हूँ shows an action in progress right now or around the current time.

• मैं हिंदी लिख रही हूँ = I am writing Hindi
• मैं हिंदी लिखती हूँ = I write Hindi / I write in Hindi / I usually write Hindi

So:

• रही हूँ / रहा हूँ / रहे हैं = progressive, ongoing action
• लिखती हूँ / लिखता हूँ = habitual or general action

This is similar to the difference between English I am writing and I write.

रही shows that the speaker is feminine singular.

In this construction, the participle agrees with the subject:

• मैं लिख रहा हूँ = said by a male speaker
• मैं लिख रही हूँ = said by a female speaker

Other forms include:

• हम लिख रहे हैं = we are writing
• वे लिख रहे हैं = they are writing (masculine or mixed group)
• वे लिख रही हैं = they are writing (all feminine)

So रही tells you the speaker is female.

हूँ is the auxiliary verb to be, meaning am.

The structure is:

• main verb stem: लिख
• progressive participle: रही
• auxiliary: हूँ

So:

• लिख रही हूँ = am writing

Compare:

• मैं लिख रहा हूँ = I am writing
• तुम लिख रहे हो = you are writing
• वह लिख रहा है = he is writing
• वह लिख रही है = she is writing

In standard Hindi, हूँ should be included here.

Hindi normally follows Subject–Object–Verb order.

So in this sentence:

• मैं = subject
• हिंदी = object
• लिख रही हूँ = verb phrase

That gives:

• मैं हिंदी लिख रही हूँ

This is different from English I am writing Hindi, where the verb comes before the object.

Hindi word order can move around for emphasis, but SOV is the default pattern.

Because not every direct object takes को.

In Hindi, को is often used with:

• specific people
• animate/specific objects
• certain kinds of emphasis or definiteness

But with many inanimate or general objects, especially in simple sentences, को is not used.

So:

• मैं हिंदी लिख रही हूँ = natural
• हिंदी here is just the direct object without को

Using को here would usually sound unnatural.

In real usage, it can often be understood as to write Hindi or to write in Hindi, depending on context.

For example:

• मैं हिंदी लिख रही हूँ could mean:
  • I am writing Hindi words/script
  • I am writing in the Hindi language

Hindi often leaves this kind of distinction to context. If someone wants to be very explicit, they might use a fuller expression, but this sentence by itself is normal and understandable.

Because many common time expressions in Hindi work without a postposition.

So Hindi often says:

• सुबह = in the morning
• शाम = in the evening
• आज = today
• कल = tomorrow / yesterday

That is why सुबह मैं हिंदी लिख रही हूँ is natural.

सुबह में is usually less natural in ordinary speech for this meaning. Most of the time, just सुबह is enough.

मैं is pronounced roughly like main in English, but with nasalization.

The mark ैं is part of the vowel spelling, and in मैं the word is pronounced with a nasal quality. It is not pronounced exactly like the English word main, but that approximation helps beginners.

So:

• मैं ≈ main (nasalized)

This is the Hindi word for I.

हूँ is pronounced approximately like hoon, but very short and with nasalization.

A rough learner-friendly guide is:

• हूँ ≈ hoon

But the final sound is nasalized, not a fully pronounced English n.

So in careful pronunciation:

• मैं हिंदी लिख रही हूँ
• roughly: main hindii likh rahii hoon

This kind of transliteration is only approximate, but it helps at the beginning.

Yes. That is also natural.

Both are fine:

• सुबह मैं हिंदी लिख रही हूँ।
• मैं सुबह हिंदी लिख रही हूँ।

The difference is mostly one of focus:

• सुबह first: emphasizes the time a bit more
• मैं first: starts more neutrally with the subject

Hindi allows this flexibility much more than English does.