الرد واضح.

In careful MSA pronunciation, it is:

ar-raddu wāḍiḥun

A few useful notes:

• الرد is pronounced ar-radd(u), not al-radd(u), because ر is a sun letter.
• ردّ has a doubled d sound.
• واضح is pronounced wā-ḍiḥ:
  • ض is an emphatic d
  • ح is a strong, breathy h sound from deeper in the throat

In normal pause at the end of speech, many speakers drop the case endings, so you may hear:

ar-radd wāḍiḥ

Because Arabic often uses a nominal sentence in the present tense, with no separate word for is/are.

So:

• الرد واضح = The response is clear

This is completely normal in Arabic.

If you wanted the past tense, Arabic would use a verb such as كان:

• كان الرد واضحًا = The response was clear

This happens because ر is one of the sun letters.

With sun letters, the ل of ال is not pronounced separately. Instead, it assimilates to the next consonant, which gets doubled.

So:

• written: الرد
• pronounced: ar-radd

In fully vocalized Arabic, you would see a shadda on ر to show this doubling effect:

الرَّدُّ

Because here واضح is the predicate of the sentence, not just an adjective attached to the noun.

So:

• الرَّدُّ واضحٌ = The response is clear

But compare that with:

• الرَّدُّ الواضحُ = the clear response

That second phrase is not a full sentence. It is just a noun phrase: response + adjective.

This is a very important distinction in Arabic:

• definite noun + indefinite adjective/predicate often gives X is Y
• definite noun + definite adjective gives the Y X / the X that is Y

Fully vocalized, the sentence is:

الرَّدُّ واضِحٌ

Those endings are:

• الرَّدُّ = -u ending
• واضِحٌ = -un ending

Why?

• الرَّدُّ is the subject of the nominal sentence, so it is nominative
• واضِحٌ is the predicate, so it is also nominative

In everyday writing, these short vowels are usually omitted, so you normally just see:

الرد واضح

Lexically, yes: واضح is an adjective meaning clear.

But in this sentence, it is functioning as the predicate of the sentence, not as an attributive adjective inside a noun phrase.

So grammatically:

• الرَّدُّ واضحٌ = a full sentence, The response is clear
• الرَّدُّ الواضحُ = a noun phrase, the clear response

That difference is one of the first big grammar patterns Arabic learners need to get comfortable with.

Because the word is really رَدّ with a shadda on د, which means the consonant is doubled.

In fully marked writing:

• رَدّ = radd

But in normal Arabic text, short vowels and shadda are often not written, so you just see:

• رد

So even though you only see one د, the correct pronunciation still has a doubled d sound.

Yes. Since واضح is describing the subject as its predicate, it agrees with it.

Here:

• الرد is masculine singular
• so واضح is also masculine singular

Examples of agreement:

• الإجابة واضحةٌ = The answer is clear
  feminine singular

• الرَّدّان واضحانِ = The two responses are clear
  dual

So the form of واضح changes depending on the noun it goes with.