Which is the longest surah and the longest ayah of the Qur'an?
The longest Sura is Al-Baqarah البقرة (Arabic for "The Cow")
consisting of 286 ayat
occupying 48 pages of currently printed mushafs (called Raas Ayah Mushafs مصحف رأس آية, it's special that every page ends with the end of the last ayah in it, so no ayah starts in a page and ends in the next page, which makes it easier while reading).
The Sura was so named (by the Prophet Muhammad (pbuh), of course) because the story of the prophet Moses (pbuh), Bani Israel, and the cow was told within it. Where Moses (pbuh) ordered them to slay a specific cow so that he can use its meat to temporarily revive a killed man and make him say who killed him, at the willing of Allah, of course.
The longest Ayah (verse) is the 282th Aya of Surat Al-Baqarah itself:
It occupies a whole page of currently printed mushafs, no other aya does.
It's called Ayat Al-Mudaianah آية المداينة (the verse of debiting, lending, borrowing, etc.) because it describes the Islamic rules of debiting money.
Some scholars say that Allah made the longest Ayah a description about debiting to show us that money exchange should be treated so carefully.
Hope that's helpful.
According to what you asked that “Which is the longest surah and the longest ayah (verse) of the Qur'an?”
In order to respond to these two questions, it can be remarked that:
1. Surah al-Baqarah is deemed as the longest surah of the holy Qur’an 2. Verse 282 of surah al-Baqarah is deemed as the longest verse of the Qur’an which is as follows:
يَا أَيُّهَا الَّذِينَ آمَنُوا إِذَا تَدَايَنتُم بِدَيْنٍ إِلَىٰ أَجَلٍ مُّسَمًّى فَاكْتُبُوهُ ۚ وَلْيَكْتُب بَّيْنَكُمْ كَاتِبٌ بِالْعَدْلِ ۚ وَلَا يَأْبَ كَاتِبٌ أَن يَكْتُبَ كَمَا عَلَّمَهُ اللَّـهُ ۚ فَلْيَكْتُبْ وَلْيُمْلِلِ الَّذِي عَلَيْهِ الْحَقُّ وَلْيَتَّقِ اللَّـهَ رَبَّهُ وَلَا يَبْخَسْ مِنْهُ شَيْئًا ۚ فَإِن كَانَ الَّذِي عَلَيْهِ الْحَقُّ سَفِيهًا أَوْ ضَعِيفًا أَوْ لَا يَسْتَطِيعُ أَن يُمِلَّ هُوَ فَلْيُمْلِلْ وَلِيُّهُ بِالْعَدْلِ ۚ وَاسْتَشْهِدُوا شَهِيدَيْنِ مِن رِّجَالِكُمْ ۖ فَإِن لَّمْ يَكُونَا رَجُلَيْنِ فَرَجُلٌ وَامْرَأَتَانِ مِمَّن تَرْضَوْنَ مِنَ الشُّهَدَاءِ أَن تَضِلَّ إِحْدَاهُمَا فَتُذَكِّرَ إِحْدَاهُمَا الْأُخْرَىٰ ۚ وَلَا يَأْبَ الشُّهَدَاءُ إِذَا مَا دُعُوا ۚ وَلَا تَسْأَمُوا أَن تَكْتُبُوهُ صَغِيرًا أَوْ كَبِيرًا إِلَىٰ أَجَلِهِ ۚ ذَٰلِكُمْ أَقْسَطُ عِندَ اللَّـهِ وَأَقْوَمُ لِلشَّهَادَةِ وَأَدْنَىٰ أَلَّا تَرْتَابُوا ۖ إِلَّا أَن تَكُونَ تِجَارَةً حَاضِرَةً تُدِيرُونَهَا بَيْنَكُمْ فَلَيْسَ عَلَيْكُمْ جُنَاحٌ أَلَّا تَكْتُبُوهَا ۗ وَأَشْهِدُوا إِذَا تَبَايَعْتُمْ ۚ وَلَا يُضَارَّ كَاتِبٌ وَلَا شَهِيدٌ ۚ وَإِن تَفْعَلُوا فَإِنَّهُ فُسُوقٌ بِكُمْ ۗ وَاتَّقُوا اللَّـهَ ۖ وَيُعَلِّمُكُمُ اللَّـهُ ۗ وَاللَّـهُ بِكُلِّ شَيْءٍ عَلِيمٌ ﴿٢٨٢﴾
O you who have believed, when you contract a debt for a specified term, write it down. And let a scribe write [it] between you in justice. Let no scribe refuse to write as Allah has taught him. So let him write and let the one who has the obligation dictate. And let him fear Allah, his Lord, and not leave anything out of it. But if the one who has the obligation is of limited understanding or weak or unable to dictate himself, then let his guardian dictate in justice. And bring to witness two witnesses from among your men. And if there are not two men [available], then a man and two women from those whom you accept as witnesses - so that if one of the women errs, then the other can remind her. And let not the witnesses refuse when they are called upon. And do not be [too] weary to write it, whether it is small or large, for its [specified] term. That is more just in the sight of Allah and stronger as evidence and more likely to prevent doubt between you, except when it is an immediate transaction which you conduct among yourselves. For [then] there is no blame upon you if you do not write it. And take witnesses when you conclude a contract. Let no scribe be harmed or any witness. For if you do so, indeed, it is [grave] disobedience in you. And fear Allah. And Allah teaches you. And Allah is Knowing of all things. (282)