Only 1 is correct. "in case" + clause is a reason clause. It's neutral and not especially informal. e.g. I will take an umbrella in case it rains = I will take an umbrella because it is possible that it will rain "in case of + noun phrase" is a conditional expression used most often on formal official notices related to safety during disasters or emergencies e.g. In case of fire, please use this fire extinguisher = If there is a fire, please use this fire extinguisher

They are the same in meaning. But "in case" is a colloquial expression while "in case of" is more formal used in official notice.

"In case of" is usually used in instructions like: in case of fire. It has some tinge of warning or something unpleasant.