For the second one, I would say: For location: The boy is in the field. For activity: The boy is running on the field.

Yes, it is normal to say "the boy is running in the race". Is that your question?.

Thanks Patrick!!! You've made it clear . And I want to ask whether 'in the track' exists. Here's the sentence-- ' Athletes are running in the ___(track/field) '. The context is that athletes are competing in a race,which means that they are supposed to be 'running ON the track ' ,but the preposition given is IN, and it makes me hesitate.

1) Runners sped up on the track. 2) There's a little boy in the field. However, #2 could go either way. If it is a field of flowers, then I would say "in the field". However, if it is a baseball field then I would say "on the field". But just to make it more confusing, for sports fields sometimes we say "he is in the field of play". I hope that helps :)