मैं सुबह चेहरा धोती हूँ।

Because the speaker is female.

In this sentence, धोती हूँ agrees with मैं when the speaker is a woman:

• मैं ... धोती हूँ = I (female) wash
• मैं ... धोता हूँ = I (male) wash

So:

• मैं सुबह चेहरा धोती हूँ। = said by a woman
• मैं सुबह चेहरा धोता हूँ। = said by a man

हूँ is the present-tense form of होना (to be) used with मैं.

In the pattern verb stem + ता/ती/ते + होना, Hindi forms the habitual present:

• मैं खाती हूँ = I eat / I usually eat
• मैं पढ़ती हूँ = I read / I usually read
• मैं धोती हूँ = I wash / I usually wash

So धोती हूँ works together as the verb phrase.

It normally means I wash my face in the morning or I wash my face every morning.

This is the habitual form, not the progressive form.

• मैं सुबह चेहरा धोती हूँ। = I wash my face in the morning / I usually wash my face in the morning
• मैं सुबह चेहरा धो रही हूँ। = I am washing my face in the morning

So the given sentence talks about a habit or routine.

In Hindi, with body parts and close personal things, the possessive is often left out when it is obvious.

So:

• मैं चेहरा धोती हूँ naturally means I wash my face
• not I wash a face

Hindi often relies on context here. Since the subject is I, it is understood that the face is the speaker's own face.

You can say:

• मैं सुबह अपना चेहरा धोती हूँ।

This adds अपना = my own, but in many everyday situations it is not necessary.

Because चेहरा is a direct object here, and direct objects in Hindi often appear without को, especially when they are:

• inanimate
• general/non-emphasized
• not being specially marked

So:

• मैं चेहरा धोती हूँ। = normal and natural

को is more common with:

• people
• animate beings
• specific/emphasized objects

For this sentence, चेहरा without को is the standard choice.

सुबह means morning or in the morning, depending on context.

In this sentence:

• मैं सुबह चेहरा धोती हूँ। = I wash my face in the morning

Hindi often does not need a separate word for in with time expressions like this.

Compare:

• सुबह = in the morning / morning
• शाम = in the evening / evening
• रात = at night / night

Because with common time words like सुबह, Hindi usually does not need में.

The most natural version is:

• मैं सुबह चेहरा धोती हूँ।

You may hear सुबह में in some speech, but for standard, natural everyday Hindi, just सुबह is usually better here.

Hindi usually prefers Subject + Time + Object + Verb or, more generally, Subject + Object + Verb.

So here:

• मैं = I
• सुबह = in the morning
• चेहरा = face
• धोती हूँ = wash

That gives:

• I + in the morning + face + wash

This is normal Hindi word order.
English puts the verb earlier:

• I wash my face in the morning

Hindi keeps the main verb at the end.

Yes. That is also grammatical.

Hindi word order is somewhat flexible, especially with time expressions. These are all possible:

• मैं सुबह चेहरा धोती हूँ।
• मैं सुबह अपना चेहरा धोती हूँ।
• मैं अपना चेहरा सुबह धोती हूँ।

The first one is simple and natural.
Adding अपना can make the sentence a bit clearer or more emphatic.

People say both, but मुँह धोना is very common in everyday speech.

• चेहरा धोना = to wash the face
• मुँह धोना = literally to wash the mouth/face, but often used in the sense of washing the face

Depending on context:

• मैं सुबह मुँह धोती हूँ। is very natural in conversation
• मैं सुबह चेहरा धोती हूँ। is also correct and clear

A man would say:

• मैं सुबह चेहरा धोता हूँ।

Only धोती changes to धोता.

So:

• female speaker: मैं सुबह चेहरा धोती हूँ।
• male speaker: मैं सुबह चेहरा धोता हूँ।

That change reflects the speaker's gender.