Fat chance
不可能，没门儿 是一种讽刺（sarcastically)的说法
A: Are you going to buy me a new coat for Christmas?
你会给我买件新外套当做圣诞节礼物吗？
B：Fat chance!
没门儿！
I think it's 50/50.
有一半的可能性
We have a 50/50 chance.
有一半的可能性
There is no hope.
几乎不可能
There is no possibility.
几乎不可能
There is no chance.
几乎不可能

Chance
是一种偶然的机会
Opportunity
是一种被给予、被许可的机会。
I was never given the opportunity of going to college.
我从来都没有机会上大学。
She left and I missed my chance to say goodbye to her
她走了，我错过了跟她说再见的机会。
This is a good opportunity to get a promotion.
这是个升职的好机会。
This is a too good chance/opportunity to be lost.
这是个不容错失的好机会。
Yes. It's my fault. So please give me a one more chance.
是我的错，请再给我一次机会。