Idioms (成语) in the HSK

The HSK curriculum has a total 112 idioms. With the exception of

讨价还价 and 名胜古迹
being in HSK 5, the rest 110 are all in HSK 6.

Idiom Period Source

There are also 9 four-character phrases in the HSK that are obviously not idioms:

公共汽车 电子邮件 高速公路 归根到底 二氧化碳 新陈代谢 烟花爆竹 迄今为止 通货膨胀