The chemical formula CH2O can be classified as Empirical formula and possibly a molecular formula. The empirical formula of a compound is the simplest formula that indicates the simplest ratio of atoms in the compound, while the molecular formula is the representation of the actual whole number ratio between the elements of the compound.
Answer: 2. cannot be an element.
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: Copper 
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: methane 

Thus as it can be decomposed into its constituent elements, it is a compound.
Mixture is a substance which has two or more components which do not combine chemically and do not have any fixed ratio in which they are present.
Thus methane cannot be an element.
Answer:
Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.
Answer:
Follows are the solution to this question:
Explanation:
Please find the complete solution in the attached file.
The solubility of NaCl in water will not be affected by an increase in pressure.
We know that the density of NaCl(s) in 2.165 g/cm³ at 25 °C and we want to know how will its solubility in water be affected when the pressure is increased.
<h3>What is solubility?</h3>
Solubility is the maximum mass of a solute that can be dissolved in 100 grams of solvent at a determined temperature.
The solubility of a solid, such as NaCl, in a liquid, is mainly affected by the temperature. However, since solids are not compressible, an increase in pressure will not affect its solubility.
On the other hand, the solubility of gases in water will increase with an increase in pressure, as stated by Henry's law.
The solubility of NaCl in water will not be affected by an increase in pressure.
Learn more about solubility here: brainly.com/question/11963573