Explain how various literary devices are used in Act I, Scene 6 of Macbeth.


In this scene, Duncan arrives at Macbeth's castle to be his guest and accept his hospitality. Shakespeare reinforces the irony of this scene every step of the way. The type of irony he uses is called dramatic irony, because the audience knows what Duncan does not: that the Macbeths plan to murder him. 

The first irony is in Duncan's description of the setting. From the very first, Duncan misreads the scene, saying

This castle hath a pleasant seat. The air
Nimbly and sweetly recommends itself
Unto our gentle senses.
"Pleasant," "sweet" and "gentle" are ironic terms in this context: the castle will be the opposite of that to Duncan. 
Duncan then greets Lady Macbeth by twice commending her "love" in putting herself out to host him. Needless to say, "love" hardly motivates Lady Macbeth, who in the last scene called on the gods to harden her heart and make her ruthless and inhuman in every fiber of her being.
What follows Duncan's speech is Lady Macbeth's reply that everything they do is to honor Duncan—he accepts this as true while the audience knows he is being sucked ever closer to his doom. The irony grows thicker as Duncan asks where Macbeth is and speaks of Macbeth's "love" for him.
An added irony is Banquo's happy response to the castle. He notes how sweet "heaven's breath" (the breeze) is at the castle and says that the birds like to make their nests in such a place:
Where they most breed and haunt, I have observed,
The air is delicate.
Later, we will come to understand the irony of these words. The castle will become anything but "delicate" towards him and not all the sweet scents of the Orient will mask the stench of blood that haunts the grounds.
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