Answer: (3) silicon
Explanation:
Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: Silicon (Si)
Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: ethane 
, propanone 
and water 
Answer:
Radiation
Explanation:
Thermal energy (heat) can be transferred between objects as long as there is a temperature difference between them. However, there needs to be some kind of medium transferring it. There are basically three ways in which the energy is transferred:
1. Conduction - transfer via the direct contact
2. Convection - transfer via the circular movement of fluids or air caused by hotter layers moving upward and colder downwards.
3. Radiation - transfer via the waves from the invisible spectrum of electromagnetic radiation ( ultra-violet, infra-red...)
Frequency is not a type of energy transfer, but a number of times something is occurring in one second. When we say that the frequency is 200Hz it means that something is happening at a rate of 200 times in a second. It's most often used in describing oscillations.
Answer:
A.
Single-celled organisms are simple, while multicellular organisms are complex.
I hope my calculation is correct :P
