Can you find out which number multiplied by itself will give the output as 12345678987654321?

Can you identify the hidden rebus in the image below?

The more you take me, the more you leave me behind.
Who Am I?

An American nightclub called 'The Coconut Grove' had a terrible fire in which over 400 people died. A simple design flaw in the building led to a high death toll. Subsequently, regulations were changed to ensure that all public buildings throughout the country eliminated this one detail, which proved deadly. What was it?

When my father was 31 I was 8. Now he is twice as old as me. How old am I?

What is common among 11, 69, and 88?

What is 3/7 chicken, 2/3 cat and 2/4 goat?

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

Can you find the number?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

Andrew’s doctor gives him three pills and tells him to take one every half hour. How much time will have passed by the time Andrew’s taken all three pills?