Answer: silicon Si, Germanium GE
Explanation:
An element is a pure substance made up of only one kind of atom. An element is composed of atoms in which it is composed of neutrons and protons. The nucleus is surrounded by electrons. The answer to this problem is A. element
<h2>
contains both covalent and ionic bonds.</h2>
Explanation:
A covalent bond is formed when an element shares its valence electron with another element. This bond is formed between two non metals.
An ionic bond is formed when an element completely transfers its valence electron to another element. The element which donates the electron is known as electropositive element or the metal and the element which accepts the electrons is known as electronegative element or non metal.
a. 
contain covalent bonds as they are made up of non metals only.
b. 
contain ionic bonds as they are made up of sodium metal and fluorine non metal.
c. 
contain covalent bonds as they are made up of non metals only.
d. contain ionic bonds between 
and 
and covalent between N and H in 
Learn more about ionic and covalent bonds
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Answer:
Option D - 10,000 years ago in the Middle East
Ni (Nickel) is the best conductor, and in fact the only conductor, in that list
