Macbeth has just heard from the Weird Sisters that Banquo's descendants will become kings, and he is upset and disturbed by this prophecy. He is also haunted by the guilt and paranoia from the murder of King Duncan. In this state of mind, he accuses Lady Macbeth of having a malicious and scheming mind, full of evil thoughts.
The phrase "full of scorpions is your mind, dear wife" is a metaphorical expression. Scorpions are known for their venomous stings, and Macbeth uses this metaphor to describe the poisonous and harmful nature of Lady Macbeth's thoughts and intentions. He believes that her mind is filled with wicked plans and desires, which are as dangerous and harmful as the stings of scorpions.
Through this metaphor, Macbeth expresses his disillusionment with Lady Macbeth. He had previously relied on her for support and encouragement in their quest for power, but now he sees her as a source of trouble and danger. He feels that she is consumed by her own ambition and ruthlessness, and he fears the consequences of her actions.
The use of the word "dear" in this line adds an element of irony. Macbeth addresses his wife as "dear," but his tone is anything but affectionate. It is a bitter and sarcastic remark, highlighting the deterioration of their relationship and the growing distance between them.
In summary, when Macbeth says "full of scorpions is your mind, dear wife," he is accusing her of having a malicious and scheming mind, filled with evil thoughts and intentions. He sees her as a source of danger and trouble, and the metaphor of scorpions reflects his belief that her thoughts are poisonous and harmful.