Is the dog ritually impure and does it expel angels from the house? Has this been mentioned in the Holy Quran, or is it one of the things that invalidate ablution? Are the hadiths regarding the impurity of the dog authentic?

The preponderant view is that dogs are impure. It is permissible to keep them for guarding and hunting. However, keeping them without need is not permissible. Moreover, those who consider them pure do not permit keeping them at all.

What some people claim, that al-Bukhari says in his Sahih that he heard the Messenger of Allah, peace and blessings be upon him, say... this statement does not exist in Sahih al-Bukhari. As for authenticating and weakening hadith, it is done according to established principles known to specialists in hadith sciences.

The Quran is definitive in its authenticity, but some of its verses are definitive in their meaning while others are probabilistic. Some are clear (muhkam) and others are ambiguous (mutashabih). The Sunnah then comes to explain and clarify it.

The Quran did not address the issue of the dog's purity. There is no necessary connection between mentioning the dog in the story of the Companions of the Cave and ruling on its purity. Being kind to a dog does not mean it is pure or that it is permissible to keep it.

There is nothing that necessitates invalidating ablution by touching a dog.

Everything that person mentioned is not sufficient for argumentation and contradicts clear evidence.