We often confuse the use of certain words, especially when the subject refers to syntactic analysis. To illustrate such an occurrence, the “what” comes into play. In this sense, let us now take care of remedying these possible misunderstandings, in order to keep ourselves well informed about the aspects that nourish the language as a whole. To do so, let's look at some examples:
It was necessary for you to come soon.
We have two clauses: the first, also called the main clause, and the second, represented by a subjective substantive subordinate clause. But how do we reach this conclusion?
Simple, because when we ask the question to the verb: what was needed? We soon discover that “you would come soon” represents the subject of the prayer in focus.
Thus, this “what” is classified as an integral conjunction because it introduces a substantive subordinate clause.
So let's look at this other example:
The students, who got good grades, are on vacation.
We note that the word “that”, this time, plays an important role: that of replacing the noun “students”. For this reason it is classified as a relative pronoun, given that it introduces a restrictive adjectival subordinate clause.
And here's a very important tip: to find out if it really is a relative pronoun, just replace it with “which, which, which, which”. Therefore, why such a classification.
By Vânia Duarte
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/que-ora-conjuncao-integrante-ora-pronome-relativo.htm