Ans is C. SELECT ID FROM Trainer_c WHERE Gym__r.Name = ‘Viridian City Gym’

Explanation:
Since Trainer_c has a lookup field to Gym_c, we can traverse the relationship to get the Gym_c record and filter it by the Name field to get the record for the Viridian City gym. Then, we can use the child relationship name "Gym__r" to access the related Trainer_c records.

Option A is incorrect because it uses the wrong child relationship name ("Trainers__r") for the Trainer_c object.

Option B is incorrect because it incorrectly queries the child object's records first, rather than the parent object's record.

Option D is incorrect because it uses the wrong child relationship name ("Trainers__c") for the Trainer_c object.

we use __r instead of __r because Trainers__c and Gym__c are related to eachother and you're trying to fetch Trainers__c from Gym__c

SELECT id, (SELECT id FROM Trainers__r) FROM Gym __c WHERE NAME ='Viridian City gym'

Answer is option D, but the child object name should have the string - '__r' to specify that It has a relationship and is a child object.

Correct Answer : SELECT Id, (SELECT Id FROM Trainers__r) FROM Gym_C WHERE Name . Viridian City Gym'

answer is : SELECT Id, (SELECT Id FROM Trainers__r) FROM Gym__c WHERE Name ='Viridian City Gym'

answer is B i think, when we use inner select with standard object we should add S like Contact Contacts, and when we use custom object in inner select we should use __r instead of __c.
i wish we get explanation

Can you please check the spelling of the answers?
thanks