My friends say that they are notified when I like a post on Facebook. I don't want this. What is the privacy option that can help me?
The privacy of your like is dependent on the privacy of your friend's post. if they only share the post with you, then you liking it will only appear in your friend's activity feed/newsfeed.
If they share it with a group of friends it will appear only in that group of friends' activity feed/newsfeed.
If they share it publicly. It will end up in all your friend's activity feed/news feed
There is an option for this, but unfortunately you cannot set it; it must be set by your friends who do not want to see your comments and likes. If you comment on or like a post that they can view, then your comment or like may appear in their News Feed unless they turn those off. To do that they can hover their pointer over your name or go to your profile/timeline, then move to the Subscribed button, and uncheck "Comments and Likes".
Of course, they will still see your comments and likes on posts that they would see anyway in their News Feed, just not a separate story about them.
There could be no privacy setting that could help you - when we "like" something, we are actively making a public statement about something. If we don't want people to know we like something, we don't publish it on the web (i.e. don't touch that "like" button).
Otherwise mark4o has the best answer: if your friends don't want to receive news about your "likes" then have to follow his instructions.