What does below chemistry rebus means?

1 + 9 + 8 = ?
considering, 28 + 8 + 92 = 10

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

Can you find out the smallest number that can be conveyed as the sum of three squares in three unique ways?

81 x 9 = 801. What must you do to make the this equation true?

In a contest, four fruits (an apple, a banana, an orange, and a pear) have been placed in four closed boxes (one fruit per box). People may guess which fruit is in which box. 123 people participate in the contest. When the boxes are opened, it turns out that 43 people have guessed none of the fruits correctly, 39 people have guessed one fruit correctly, and 31 people have guessed two fruits correctly.
How many people have guessed three fruits correctly, and how many people have guessed four fruits correctly

In which direction should the missing arrow point?

I am dry when I go inside, but wet when I am pulled outside.
The longer I am inside, the stronger I get
When I am completely out, I am wet and I literally sag
Who am I?

Can you figure out the logic I used to decide the order of the following words:
gun, shoe, spree, door, hive, kicks, heaven, gate, line, den