What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

Count the number of squares in the picture below.

In a concert, Christina is performing a dance show with her group.
At 10:00, she and her crew were dancing in an absolutely straight line. At that time Christina was standing in 4th position from both the front and back end of the row.

What was the size of her crew?

You are on your way to visit your Friend, who lives at the end of the hill. It is his birthday, and you want to give him the cakes you have made. Between your house and his house, you have to cross 5 bridges, and as it goes in the land of make believe, there is a troll under every bridge! Each troll, quite rightly, insists that you pay a troll toll. Before you can cross their bridge, you have to give them half of the cakes you are carrying, but as they are kind trolls, they each give you back a single cake. How many cakes do you have to leave home to make sure that you arrive at a friend's house with exactly two

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

What question can you never answer yes to?

If 5 cats catch 5 mice in 5 minutes, how long will it take one cat to catch a mouse?

You have a basket containing ten apples. You have ten friends, who each desire an apple. You give each of your friends one apple.
Now all your friends have one apple each, yet there is an apple remaining in the basket.
How?

Find the next number in the series below.

6 18 270 72090 ?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211