Can You Recite a Longer Surah in the Second Rak`ah?
Question

What is the ruling on someone who offers a prayer and recites Surat An-Nas (no. 114) in the first Rak`ah, then in the second Rak`ah he recites Surat Ad-Duha (no. 93)? 
In other words, he starts with a short Surah and follows it in the second Rak`ah with a longer one. Is that wrong? What is the Islamic ruling concerning that?
Praise be to Allah.Is it Sunnah to recite in accordance with the sequence of Surahs in the Quran? 
The Sunnah is for the worshipper to recite in accordance with the sequence of Surahs in the Quran , but if he does not follow that sequence, there is no blame on him and his prayer is still valid, although what he has done is contrary to what is best. 
An-Nawawi (may Allah have mercy on him) said: 
“Our companions said: The Sunnah is to recite in accordance with the sequence of Surahs in the Quran , one after another. So if he recites a Surah in the first Rak`ah, he should recite in the second Rak`ah the Surah that comes immediately after it. Al-Mutawalli said: Even if he recites “Qul A`udhu  bi Rabb in-Nas” (i.e., Surat an-Nas, the last Surah in the Quran) in the first Rak`ah, in the second Rak`ah he should recite the opening verses of Al-Baqarah. If he recites a Surah then in the second Rak`ah he recites the Surah that precedes it, this is contrary to what is best, but there is no blame on him. And Allah knows best.” (Sharh Al-Muhadhdhab, 3/348) 
Can you recite a longer surah in the second Rak`ah?
The Sunnah is for the imam or the person who is praying on his own to recite in the first Rak`ah a Surah that is longer than what he recites in the second Rak`ah, because of the report narrated by Abu Qatadah (may Allah be pleased with him), according to which the Prophet (blessings and peace of Allah be upon him) used to recite in the first two Rak`ahs of Dhuhr, Al-Fatihah and two Surahs, and in the last two Rak`ahs he recited Al-Fatihah (only), and he would make the first Rak`ah lengthy but the second not as long. And he did likewise in `Asr and Fajr. (Narrated by Al-Bukhari, 734 and Muslim, 685) 
Ibn Qudamah (may Allah have mercy on him) said: 
“It is recommended to make the first Rak`ah lengthy in all prayers, so that the one who wants to join the prayer may (have time) to do so… because of the Hadith of Abu Qatadah (may Allah be pleased with him). Ahmad (may Allah have mercy on him) said, concerning the imam who makes the second Rak`ah longer than the first: He should be told to go and learn. He also said, concerning the imam who makes the first Rak`ah short and the second long: This is not appropriate; he should be told to follow the Sunnah.” (Al-Mughni, 1/334)
The scholars of the Standing Committee (6389) were asked: 
Is it permissible when reciting during the prayer to make the first recitation a short Surah or a lengthy Surah? Many people recite a short Surah in the first Rak`ah and a longer one in the second. 
They replied: 
“The Sunnah is to recite in the first Rak`ah after Al-Fatihah a longer Surah than in the second Rak`ah, because of the report narrated by Abu Qatadah (may Allah be pleased with him) … And they quoted the Hadith referred to above. But if he makes them of equal length or he recites a longer Surah in the second Rak`ah, there is nothing wrong with that, because the Prophet (blessings and peace of Allah be upon him) did that sometimes, as it is proven that he (blessings and peace of Allah be upon him) used to recite in Jumu`ah prayer Al-A`la (no. 87) and Al-Ghashiyah (no. 88), and Al-Ghashiyah is slightly longer.” (Al-Lajnah Ad-Da’imah lil-Buhuth Al-`Ilmiyyah wal-Ifta’, Shaykh `Abd Al-`Aziz ibn `Abdullah ibn Baz, Shaykh `Abd Ar-Razzaq `Afifi, Shaykh `Abdullah ibn Ghadyan, Shaykh `Abdullah ibn Qa`ud)
Shaykh Ibn Baz (may Allah have mercy on him) was asked: What is the ruling if the imam recites in the first Rak`ah of the prayer, for example, Surat Al-Ikhlas (no. 112) then in the second Rak`ah he recites Ad-Duha (no. 93)? 
He replied: 
“There is nothing wrong with the Imam reciting in the first Rak`ah less than he recites in the second, because of the general meaning of the words of Allah, may He be Glorified:
“So recite as much of the Quran as may be easy (for you)” [Al-Muzzammil 73:20].
And the general meaning of the words of the Prophet (blessings and peace of Allah be upon him) to the one who prayed badly: “When you get up to pray, do Wudu’ properly, then turn to face the Qiblah, say Takbir, then recite as much as you are able to of Quran.” According to another version: “Then recite Al-Fatihah and whatever Allah wills…” 
But by doing so, he has omitted to do what is preferable, because the confirmed Sunnah, from the words and deeds of the Prophet (blessings and peace of Allah be upon him) indicates that the Sunnah, both for the imam and one who is praying on his own, is to recite a longer portion in the first Rak`ah than in the second, in all five prayers. As for one who is praying behind an imam, he should follow his imam.” (Majmu` Al-Fatawa, 11/83) 
For more details, please see the following answers: 20043 , 6422 , and 97484 . 
And Allah knows best.