Hello Aspirant.

Really sorry, but  your question is not complete and that's why it's not clear to me and you've also not mentioned about the exam for which you are asking but I guess that you are asking that what does 1g refer in answer key? So let me tell you that there are various abbreviations that are given in answer key of different competitive exams and 1G is one of them and it is used to denote  the reserved category people basically, it refers to the students who fall under 1A category and do not live in rural areas.{1A is the category for Rural Students.}

HOPE THIS HELPS YOU.

GOOD LUCK AND STAY MOTIVATED.

Thankyou.