Pleasee help I have a test!

What causes different colors to appear in the sky? the absorption of light by air molecules the reflection of light by bodies of water the greenhouse effect in earth's atmosphere the scattering and reflection of light by dust particles

Why is any chemical reaction always balanced? give reasons and explain the easiest way to solve the balancing problems in chemical equations with stoichiometric coefficients upto 20 as hit and trial doesn't always work. give full reasoning

Sodium chloride can be made as follows: 2na + cl2 ? 2nacl i calculate the maximum amount of nacl possible if 2.3 g of sodium was reacted with excess chlorine. show all your workings.