The word(s) "certainly" appears 150 time(s) in 144 verse(s) in Quran in Mohsin Khan translation.

(11) This is because of that (evil) which your hands have sent before you. And certainly, Allah is never unjust to (His) slaves.

(12) You shall certainly be tried and tested in your wealth and properties and in your personal selves, and you shall certainly hear much that will grieve you from those who received the Scripture before you (Jews and Christians) and from those who ascribe partners to Allah; but if you persevere patiently, and become Al-Muttaqun (the pious - See V.2:2) then verily, that will be a determining factor in all affairs (and that is from the great matters which you must hold on with all your efforts).

(13) And there are, certainly, among the people of the Scripture (Jews and Christians), those who believe in Allah and in that which has been revealed to you, and in that which has been revealed to them, humbling themselves before Allah. They do not sell the Verses of Allah for a little price, for them is a reward with their Lord. Surely, Allah is Swift in account.

(14) There is certainly among you he who would linger behind (from fighting in Allah's Cause). If a misfortune befalls you, he says, "Indeed Allah has favoured me in that I was not present among them."

(15) When you are greeted with a greeting, greet in return with what is better than it, or (at least) return it equally. certainly, Allah is Ever a Careful Account Taker of all things.

(16) And seek the Forgiveness of Allah, certainly, Allah is Ever Oft-Forgiving, Most Merciful.

(17) Had not the Grace of Allah and His Mercy been upon you (O Muhammad صلى الله عليه وسلم), a party of them would certainly have made a decision to mislead you, but (in fact) they mislead none except their own selves, and no harm can they do to you in the least. Allah has sent down to you the Book (The Qur'an), and Al-Hikmah (Islamic laws, knowledge of legal and illegal things i.e. the Prophet's Sunnah - legal ways), and taught you that which you knew not. And Ever Great is the Grace of Allah unto you (O Muhammad صلى الله عليه وسلم).

(18) Verily, I will mislead them, and surely, I will arouse in them false desires; and certainly, I will order them to slit the ears of cattle, and indeed I will order them to change the nature created by Allah." And whoever takes Shaitan (Satan) as a Wali (protector or helper) instead of Allah, has surely suffered a manifest loss.

(19) And it has already been revealed to you in the Book (this Qur'an) that when you hear the Verses of Allah being denied and mocked at, then sit not with them, until they engage in a talk other than that; (but if you stayed with them) certainly in that case you would be like them. Surely, Allah will collect the hypocrites and disbelievers all together in Hell.

(20) Verily, those who disbelieve [by concealing the truth about Prophet Muhammad صلى الله عليه وسلم and his message of true Islamic Monotheism written in the Taurat (Torah) and the Injeel (Gospel) with them] and prevent (mankind) from the Path of Allah (Islamic Monotheism); they have certainly strayed far away. (Tafsir Al-Qurtubi).