It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

Can you fill the blank with the correct number?

6 30 870 756030 _____

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

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

A bomb goes off.
Carnage.
One person, only a few feet away, survives! How can this be?

You see me once in June, twice in November, and not at all in May. What am I?

I am green and found in the forest and have needles instead of leaves. What am I?
Hint 1: It can be used for Christmas decorations.
Hint 2: I have a strong, scent that is used in air fresheners.

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

I am a five-letter word and comprises two different vowels and three same consonants. I am so strong that I can spoil your entire work.

Can you find out who am I?

Can you count the number of triangles in the given picture?