What is the ruling on a wife throwing a copy of the Quran onto a chair next to her—not on the ground—when angry, and what is incumbent upon the husband who then abandoned her and spoke harshly to her out of reverence for the Book of Allah?

Throwing the Mushaf (Qur'an) is a great evil and a serious crime. It indicates hatred for the Book of Allah or contempt for it, and all of that is disbelief (kufr) and apostasy (riddah), unless the anger is so severe that it leads to a loss of consciousness, in which case the person is excused. If the anger does not reach this degree, then the sin is great, and the person must repent.

Although your wife's throwing of the Mushaf might have been due to her daughter's mistake and not out of contempt, throwing it is still an evil act in any case, for the Mushaf deserves veneration. Perhaps Allah will forgive her due to her anger.

Sheikh Ibn Baz cited the story of Musa (peace be upon him) as evidence for excusing someone who loses consciousness due to anger. Musa threw down the Tablets and dragged his brother Harun out of intense anger, and Allah did not hold him accountable for that, because his anger was intense for the sake of Allah. Ibn Baz opines that divorce or cursing by someone whose anger is severe does not take effect and does not constitute apostasy, because his intention is clouded, and he resembles one who is insane.