A while ago, I submitted a first paper and it has been Under Review for a while. After submitting the paper, I was already working on another paper, which is related to the first one and requires giving it proper reference.
Currently, I have finished the second paper and I'm confused between two options:
1- Waiting for the first paper to get published (in case of acceptance) and then give proper reference to it in the second paper and proceed to submit.
2- Proceed to submit the second paper without giving proper reference to the first (since it has not yet been published), and hope that the decision on the first paper will be received so that I can give proper reference in the revised version of the second paper.
Which one of the two options is reasonable and ethical?
NB 1: Note that the results of the second paper do not make those of the first useless, and each paper has its own results.
NB 2: No preprint option is available from the first journal.