grammatical problem，need help！！ problem

青青狼

我想请教各位前辈一些语法。
1） He was the leader on which/who we relied .       He was the leader which/who we relied on.


以上有语法上的错误吗？

2）The game we are enjoying.
       Material we can use.
以上有语法上的错误吗？

3) Fetch me that pen that belongs to Ali.
Fetch me that pen Which belongs to Al
that 和which 可以互换使用吗？

4)X is the numeric value at which to evaluate the distribution.
如果我把at 去掉，可以吗？

tingroom

第一个我感觉要提前的。
第二个没错误
第三个用which