What is the standard number of references a paper should have?

Regarding the number of reference citations, there is no specific number or range that is considered as normal or standard.

The main point to take into consideration is to answer this question:

What is the purpose of referencing and reference list?

A reference list should consist of everything that is cited in a manuscript, whether in paraphrases or in direct quotes. It allows the author to credit the work of others that directly influenced the present work and document any facts that are not common knowledge. In addition, it gives interested readers the information necessary to identify and retrieve those sources.

Consider the following questions in order to check whether the numbers of provided references credit your manuscript or not.

1. Are there any key points in the manuscript you left without scientific evidence?
2. Do you rely too muchon any source? Do you use 2 or 3 sources merely to improve the validity of the research findings?
3. If there are statements without scientific evidence in the paper, is it possible to refer to the available sources?
4. If there are controversies about the research problem, are both for and against views mentioned?