What does this simple rebus mean?

Can you place six X (crosses) in below board without making three in a row in any way ?

A bridge is about to collapse. There are four people P, Q, R and S on one of the sides. Before the bridge collapses, they want to cross it. Now since the bridge is too weak, it can only stand the weight of two people at a time. Also, it is night time and nothing is visible. They have just one torch with them.

Now P takes one minute to cross the bridge, Q takes two minutes to cross, R takes five minutes to cross and S takes ten minutes to cross.

The bridge will collapse in seventeen minutes. How will they be able to cross the bridge before it collapses?

When you stop to look, you can always see me. But if you try to touch me, you can never feel me. Although you walk towards me, I remain the same distance from you. What am I?

What has a bottom at the top?

Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

What's a single-digit number with no value?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

In the following picture, E is going to slide the object down and as per the terrain and the physics, the round object is going to travel all the way till the end. Now, can you analyze who all people will die when it happens?

Replace all '*' with digits 1, 2, 3, 4, 5 and 6 to make below statement true.

* *
x *
=====
* * *