Answer: The statement conjugate base of hydrofluoric acid is weaker than that of acetic acid is most likely true.
Explanation:
A strong acid upon dissociation gives a weak conjugate base. This can also be said as stronger is the acid, weaker will be its conjugate base or vice-versa.
Hydrofluoric acid is a strong base as it dissociates completely when dissolved in water.
For example, 
The conjugate base is
which is a weak base.
Acetic acid is a weak acid as it dissociates partially when dissolved in water. So, the conjugate base of acetic acid is a strong base.

Thus, we can conclude that the statement conjugate base of hydrofluoric acid is weaker than that of acetic acid is most likely true.
Answer:
Greater
Explanation:
According to the law of universal gravitation, the force of gravitation is directly proportional to the product of the masses of the two objects and INDIRECTLY proportional to the square of the distance. In short, the bigger the masses, the stronger the gravitational force, the lesser the distance between the two objects, the greater the gravitational force.
Pure substances contain a single type of chemical species, either element or compound. Elements cannot be further broken into simpler units by chemical methods. If we consider a sample of elements, it has a single type of atoms present in it. A compound has one or more atoms bound together chemically. Compounds can be broken down into simpler units by chemical means. When we consider a sample of a single compound say water, it has all the pure water molecules. Hence, elements and compounds are pure substances.
c. sandstone in the zone of saturation
Explanation:
The best aquifer of all is a sandstone in the zone of saturation. An aquifer is a porous and permeable formation where groundwater can accumulate.
- To be a good aquifer, a rock or soil must be porous and permeable.
- Porosity is the amount of void spaces present in a rock.
- Permeability is the inter-connectivity of the pore spaces.
The zone of saturation is the zone below the water table where water is always present underground.
- Sandstones have high porosity and permeability.
- They are good aquifers when found at the zone of saturation.
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Answer: Ionic bonds form only between metals and nonmetals. That's because metals “want” to give up electrons, and nonmetals “want” to gain electrons. It takes energy to remove valence electrons from an atom and form a positive ion. Energy is released when an atom gains valence electrons and forms a negative ion