What does below chemistry rebus means?

The below given figure comprises of a pattern through which you can determine the missing letter. Can you push your mind to find the pattern and add the missing letter?

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

On my way to St. Ives I saw a man with 7 wives. Each wife had 7 sacks. Each sack had 7 cats. Each cat had 7 kittens. Kittens, cats, sacks, wives. How many were going to St. Ives?

The sum of a mother, her baby and her dog's weight is 170 Kg. How much does the baby weigh if the mother weighs 100 kg more than the combined weight of the baby and the dog, and the dog weighs 60 per cent less than the baby?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?

Kareena is older than Bipasha. Bipasha is younger than Karishma and younger than Katrina. Katrina is older than Kareena and Alonso, who are older than Karishma.If Alonso and Kareena are twins, who's oldest?

what does the below math rebus puzzle mean?

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

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