An Ionic bond is when you have a metal and a nonmetal element bonded together. In this kind of bonds, the metal atom takes electrons from the nonmetal. on other words, this bond involves the gaining and losing of electrons. The atom that receives the electrons becomes an anion (negatively charged ion) and the one that loses them becomes the cation (positively charged ion)
A covalent bond is a bond created between two nonmetals element. In here, both atoms share the electrons.
Both bonds involve interaction between atoms.
Answer: a) Temperature of 
b) 
c) dehydrating agent
Explanation:
Ethanol is heated with an excess of concentrated sulfuric acid at a temperature of 170°C to produce ethene.
The balanced chemical reaction is:

Here concentrated sulfuric acid removes a water molecule from ethanol and thus acts as a dehydrating agent.
Answer:
E) Silver, mass = 420 g, d = 10.5 g/cm.
Explanation:
Hello,
In this case, since the density is defined by:

Given the mass and density, we compute the volume via:

Thus, for each vase we have:
A) 
B) 
C) 
D) 
E) 
In such a way, the largest volume corresponds to E) Silver, mass = 420 g, d = 10.5 g/cm.
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Answer: a)neptunium b) the element is unstable
Explanation:
a) 238 0 239 -1
U + n = Np e
92 1 93 0
b) it is an isotope of neptunium with half-lives less than 4.5 days, with most less than 50 minutes. It is therefore not stable that's why they where unable to identify it
Answer:
it would do wonders for the health of those using them and, by extracting energy from the fuel more efficiently, would be more environmentally sustainable too.