How many words can a pen with half refill write?

What does below chemistry rebus means?

Which of the following words don't belong in the group and why?
CORSET, COSTER, SECTOR, ESCORT, COURTS

An octopus has 8 legs. A hippogriff has 6 legs and 2 pairs of wings. A sphinx has 6 legs and one pair of wings. Now we have all 3 kinds and a total of 18 insects in a cage. We have a total of 118 legs and 20 pairs of wings. How many insects do we have of each kind?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

What has many keys but can’t open a single lock?

I go up and I go down.
I go up towards the beautiful sky and down toward the green ground.
I am present tense.
I am past tense too
Children love me.

Who Am I?

A horse was tied to a rope 5 meters long and the horses food was 15 meters away from the horse. How did the horse reach the food?

There are three Athletes (John, Tarun and Harish) and their individual Coaches (Jacob, Meenaxi and Priyanka) standing on the shore.
No Coach trusts their Athlete to be near any other Coach unless they are also with them.
There is a boat that can hold a maximum of two persons.
How can the six people get across the river?