I agree with Ashley's correction, but I wanted to add a couple of things if that's okay.

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My New Vocabulary for Today : Part 17

Notes: The phrase "don't be such a grouch" is pretty informal. I wouldn't use this with your superiors  - it can come off a little condescending. You would mostly hear this being used between friends or people you are more informal with.

If it's an informal conversation, the word "conversation" might be better than "discussion." The word "discussion" used correctly, it's just not often used to describe a more informal talk between friends.

2) He admits he did it, instead of denying it.

Notes: You could also switch that up! "Instead of denying it, he admits he did it." Both sentences are alright.

3) If it weren't for you, he would still be alive.

4) Make up your mind, what's going on.?

Notes: Technically, there should be a question mark at the end of a sentence that asks a question. So, if you're having a test and somebody asks you to write a question in English, you should end it with a period.

However, there are instances where people will end a question with a period instead. By ending a question with a period instead of a question mark, there's a different connotation. This is usually seen more in literature (when authors play around with grammar and punctuation to convey different meanings and feelings) and more informal writing/texting/blogging.

For example:

• "What is that?" This sentence means that you're wondering what "that" is.
• "What is that." By changing punctuation, there's a connotation that the question is more rhetorical.

Another example:

• "Could you turn off the light?" You're asking for someone to turn off the light.
• "Could you turn off the light." You're still asking for someone to turn off the light, but this comes off a little more curt, almost a little bit snappish.

5) It looks familiar before., so I can handle it.

Notes: I agree with Ashley.

An object or person can be similar to something or someone else. Something similar resembles something else.

• "A crocodile looks similar to an alligator."
  

If something is familiar to you, you know something about it.

• "That words looks familiar to me." You know you've seen that word before - you may not know what it means, but you recognize it.
• "He heard a familiar voice." He heard a voice that he recognizes.

6) He has was arrested by a guilty of for vandalizing a park.

Notes: I agree with Ashley's corrections.

7) A The detective has been so cranky because he couldn't find any suspect's trace at all.

Notes: You're referring to a specific detective, so it'd be better in this sentence to use "the detective" instead of "a detective."

8) Any casualty who had injured by the accident is exempted from military service.

Notes: To include all the words, you could say, "Those who became casualties were exempted from military service."

9) Normally, people with disabilitiesy are exempted from tax liability.

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Good job! Your writing is pretty good!

My New Vocabulary for Today : Part 17

(familiar isn't used quite like this, you would say "this looks familiar" or "this looks familiar, so I can handle it" but if you want to reference a previous time "Before" A native speaker would use "Similar")

6) He has arrested by a guilty of vandalizing a park. (He was arrested for vandalizing a park.) (He was arrested for vandalizing a park and found guilty.)

7) A detective has been so cranky because he couldn't find any suspect's trace at all. (The detective has been so cranky because he couldn't find the suspect's trace at all.)

8) Any casualty who had the accident is exempted from military service.  (I am not sure what you are trying to say here sorry) 

9) Normally, people with disability are exempted from tax liability. ( Normally, people with a disability are exempted from tax liabilities)