by radiation from the Earth's surface
Answer:
NaCl
Explanation:
Thus, for the compound between Na + and Cl −, we have the ionic formula NaCl (Figure 3.5 "NaCl = Table Salt").
<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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In the periodic table, there are seven horizontal rows of elements called periods.