The word(s) "hard" appears 35 time(s) in 32 verse(s) in Quran in Abdullah Yusuf Ali translation.

(21) Or, Who has created the heavens and the earth, and Who sends you down rain from the sky? Yea, with it We cause to grow well-planted orchards full of beauty of delight: it is not in your power to cause the growth of the trees in them. (Can there be another) god besides Allah? Nay, they are a people who swerve from justice.

(22) And We produce therein orchard with date-palms and vines, and We cause springs to gush forth therein:

(23) Is one whose heart Allah has opened to Islam, so that he has received Enlightenment from Allah, (no better than one hard-hearted)? Woe to those whose hearts are hardened against celebrating the praises of Allah! they are manifestly wandering (in error)!

(24) The same religion has He established for you as that which He enjoined on Noah - the which We have sent by inspiration to thee - and that which We enjoined on Abraham, Moses, and Jesus: Namely, that ye should remain steadfast in religion, and make no divisions therein: to those who worship other things than Allah, hard is the (way) to which thou callest them. Allah chooses to Himself those whom He pleases, and guides to Himself those who turn (to Him).

(25) Gives a little, then hardens (his heart)?

(26) Hastening, with eyes transfixed, towards the Caller!- "hard is this Day!", the Unbelievers will say.

(27) Has not the Time arrived for the Believers that their hearts in all humility should engage in the remembrance of Allah and of the Truth which has been revealed (to them), and that they should not become like those to whom was given Revelation aforetime, but long ages passed over them and their hearts grew hard? For many among them are rebellious transgressors.

(28) O Prophet! Strive hard against the Unbelievers and the Hypocrites, and be firm against them. Their abode is Hell,- an evil refuge (indeed).

(29) As to these, they love the fleeting life, and put away behind them a Day (that will be) hard.

(30) Further, he turned his back, striving hard (against Allah).