I’m lighter than air but a room full of me can still make you die. What am I?

The more you take from me, the bigger I get. What am I?

I orbit a star, have no light of my own, and may or may not have life. What am I?

I grow but don’t live, I melt but don’t burn. What am I?

I am found in you, and all around you. You breathe me, but too much can harm you. What am I?

I reflect light but I'm not a mirror. I show the sky, but I'm not up high. What am I?

You can't see me, but I make things move. I push and pull without a touch. What am I?

I have keys but no locks, I have space but no room. You can enter but not go outside. What am I?

I help your bones stay strong, I’m in milk and teeth belong. What element am I?

I'm found in cells, and I hold the code. What am I?