'Imperative' means vital, crucial, and essential. So, its antonym is unimportant.
Dissuade means to discourage. So, its antonym is 'persuade,' which means to encourage.
Soggy means wet, so dry is its antonym.
Solder means to join together, and thus separate is its antonym.
Solicitous means caring, concerned or someone who shows interest in a person's well-being. So, its antonym is apathetic which means uncaring.