Of all her works, this play is the most dependent on the dramatic conventions of the author’s day: it was both the least __ experimental ___ of her plays and the most commercially successful.
Source: GRE Preparation
Filling the blank is easy, but I don't understand the grammar of this sentence. What is "this play is the most dependent on" ? What's the object of this sentence? Also, shouldn't there be "one" (or, "play") after experimental and successful?
..."of all her plays, it's the most dependent on..."
This means that her plays depend to some varying degree on the current dramatic conventions. Then, within that variation of dependence, the mentioned play is more dependent than all her other plays. The purpose of the sentence is to compare this one of her plays with the other ones.
You could put "one" after both "experimental" and "successful", but it is not necessary, and it reads better without "one".
Consider a simpler example:
a: Of all her plays, this is the best one.
b: Of all her plays, this is the best.
Example b means the same as a, and it's more idiomatic.
The structure of the sentence is "Subject - linking verb - complement" (there is no object) Ie. "SVC"
The subject and linking verb are "this play" and "is".
The complement is the phrase "the most dependent on the dramatic conventions of the author's day".
In SVC sentences, the complement can be a noun phrase, a prepositional phrase or an adjective phrase.
It is common with superlatives to use the superlative form as a noun, without "one". So it is correct to say "This apple is the best" You don't need to say "This apple is the best one." And similarly you can say "This play was the most experimental". You don't need to use the word one.
