Questions & Answers about zhège rènwu hěn zhòngyào.
个 is a measure word (also called a classifier).
In Mandarin, when you say this + noun or that + noun, you usually need a measure word between them:
- 这 + 个 + 任务
- 那 + 个 + 人
- 这 + 本 + 书
So 这个任务 literally looks like:
- 这 = this
- 个 = a general measure word
- 任务 = task / mission
For many nouns, 个 is the most common general classifier, and it works fine here.
In standard Mandarin, the usual form is 这个任务.
Sometimes in casual speech, especially in some regional styles, people may drop the measure word and say something like 这任务, but learners should generally use 这个任务 because it is the safest and most standard choice.
So for now, treat 这个任务 as the normal pattern.