Word + 性 (-ness / -ity)

How safe is it?

• A report compares two electric cars on several qualities.
• this这zhèsection款kuǎnwar chariot (archaic)车chē(modifier / structural particle)的desecurity安全性ān quán xìngvery很hěnhigh高gāo。 — "This car's safety is very high."

Word + nature性xìng = -ness, -ity

• nature性xìng turns a word into an abstract quality noun: safe安全ān quán → security安全性ān quán xìng (safety), important重要zhòng yào → importance重要性zhòng yào xìng (importance), maybe / possible可能kě néng → possibility可能性kě néng xìng (possibility).
• It is common in formal writing, reports and science.

this matter's这件事zhè jiàn shì的deimportance重要性zhòng yào xìng。

Describing and comparing qualities

• rain下雨xià yǔ(modifier / structural particle)的depossibility可能性kě néng xìngvery很hěnbig大dà。 — "The chance of rain is high."
• this这个zhè geto work工作gōng zuò(modifier / structural particle)的deflexibility灵活性líng huó xìngfairly / rather比较bǐ jiàovariant of 强强qiáng。 — "This job is fairly flexible."

rain下雨xià yǔ的depossibility可能性kě néng xìngvery很hěnbig大dà。

A noun, not an adjective

nature性xìng versus to estimate度dù

• to estimate度dù also forms quality nouns, often measurable: speed速度sù dù (speed), difficulty难度nán dù (difficulty), temperature温度wēn dù (temperature).
• nature性xìng is for abstract properties: security安全性ān quán xìng, necessity必要性bì yào xìng.

this这zhè(measure word)道dàoquestion题tí的dedifficulty难度nán dùvery很hěnhigh大dà。

Recap

Read the full reference: HSK 6 grammar — Nouns.