Observation : a piece of info we all gather through our 5 senses
Hypotheses: a testable explanation for an observation
Data: info that scientists gather during an experiment
Experiment: a procedure that is designed to test a hypothesis
Conclusion a judgment or decision
Scientific method a series of steps
Answer:
Ka = 
Explanation:
Initial concentration of weak acid =
pH = 6.87
![pH = -log[H^+]](https://tex.z-dn.net/?f=pH%20%3D%20-log%5BH%5E%2B%5D)
![[H^+]=10^{-pH}](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D10%5E%7B-pH%7D)
![[H^+]=10^{-6.87}=1.35 \times 10^{-7}\ M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D10%5E%7B-6.87%7D%3D1.35%20%5Ctimes%2010%5E%7B-7%7D%5C%20M)
HA dissociated as:

(0.00045 - x) x x
[HA] at equilibrium = (0.00045 - x) M
x = 
![Ka = \frac{[H^+][A^{-}]}{[HA]}](https://tex.z-dn.net/?f=Ka%20%3D%20%5Cfrac%7B%5BH%5E%2B%5D%5BA%5E%7B-%7D%5D%7D%7B%5BHA%5D%7D)

0.000000135 <<< 0.00045

Molecules with a plane of symmetry between the chiral centers are achiral and meso. From the given molecules (Picture attached) only (A) compound 1 is meso.
When compounds possess a plane of symmetry between the chiral centers they are called achiral or meso compounds. Among the given compounds (A) compound 1 have a plane of symmetry. So we can say compound one is a meso or achiral compound. Compounds two, three, and four have no plane of symmetry, as you can see in the structures attached. So all other compounds (compound 2, compound 3, and compound 4) except compound one are not meso or achiral.
You can also learn about meso compounds from the following question:
brainly.com/question/29022658
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C. PH3 represents a compound commonly known as phosphine, whose IUPAC name is phosphorus trihydride.
<h3>What type of bond is PH3?</h3>
The electronegativity of PH3 found in the Periodic Table of the Period attracts covalent electron pairs and creates covalent bonds. However, because the electrons are not bound, asymmetrical rate distribution occurs. Therefore, PH3 is a polar molecule with a non-polar covalent bond and currently has no polar bond.
<h3 /><h3>What defines a covalent bond?</h3>
A covalent bond consists of sharing one or more electron pairs between two atoms. These electrons are attracted to two nuclei at the same time. Covalent bonds are formed when the difference in electronegativity between two atoms is too small for electron transfer to form ions.
Click here for more information on covalent bonds brainly.com/question/12732708
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The density of it would be 57. Do the math and apply the formula to it and you would get this answer.