When woman is allowed to ask divorce?

Re: When woman is allowed to ask divorce?

but we ignore it…to avoid disputes…

And of His signs is that He created for you from yourselves mates that you may find tranquillity in them; and He placed between you affection and mercy. Indeed in that are signs for a people who give thought. (21)
Surah Ar-Rum…

so what if both are not merciful each other any more…?no peace in marriage…

@KKF…yeah these reasons what I know…

waisye i always thank Allah for giving us option of Khula…because few people expect us to live miserably no matter how hard is to live…no mercy no love no respect…