the use of ,although ,when ,if

Although is a subordinator. The GMAT won't accept a sentence made with just a subordinate clause and nothing else. We'll just say that at least one independent "SV combination" needs to be present in the sentence. The important point to remember in this case is that the subordinate clause (the one that although introduces) does not always need an "SV combination".

Although with SV combinations on both sides
Although he was scared, Chetter kept walking. [correct]
Chetter kept walking, although he was scared. [correct, although can be placed in the middle as well]
Chetter kept walking although he was scared. [correct, the comma is optional when the although comes second]
Although he was scared Chetter kept walking. [incorrect, the comma is not optional when although comes before the independent clause]

Although without an SV combination in the subordinate clause
Although scared, Chetter kept walking. [correct, clause uses a verb form]
Chetter, although scared, kept walking. [correct, clause uses a verb form]
Although controversial, the deal eventually did go through. [correct, even a verbless clause is fine when although is positioned before or in the middle of the independent clause]
The deal, although controversial, eventually did go through. [correct, even a verbless clause is fine when although is positioned before or in the middle of the independent clause]
The deal eventually did go through, although controversial. [incorrect, although used in the second half without an SV combination]
Chetter kept walking, although scared. [incorrect, although used in the second half without an SV combination]