Final answer:
Lady Macbeth advises Macbeth to smile and appear innocent to deceive others, corresponding to Option 2: Macbeth should smile to deceive others.
Step-by-step explanation:
The advice that Lady Macbeth gives to Macbeth regarding his facial expressions during the murder is to deceive others by appearing innocent. She counsels him to look like an innocent flower but be like the serpent under it. This is highlighted in her statement, "Your face, my thane, is as a book where men May read strange matters. To beguile the time, Look like the time; bear welcome in your eye, Your hand, your tongue: look like the innocent flower, But be the serpent under't." This advice from Lady Macbeth directly corresponds to Option 2: Macbeth should smile to deceive others. She emphasizes the importance of presenting a welcoming and harmless demeanor to avoid suspicion while concealing the treachery in their hearts.