Which of these elements has the lowest melting point? (1) Li (3) K (2) Na (4) Rb

2 answers:

4 0

The answer is (4) Rb. From observation, we can find that these four elements are from first column. The melting point from top to the bottom is from high to low. So the answer is (4).

natali 33 [55]3 years ago

4 0

Answer: Option (4) is the correct answer.

Explanation:

It is known that on moving down a group there will be decrease in melting point of the element because of increase in number of shells.

As a result, outermost electrons move away from the nucleus due to which there will be decrease in force of attraction between the protons and valence electrons. Hence, there will be decrease in melting point.

Therefore, the given elements are of same group and Rb has largest atomic size.

Thus, we can conclude that Rb has the lowest melting point.

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What is the concentration (in M) of a sample of the unknown dye with an absorbance of 0.25 at 542 nm?

Sladkaya [172]

Answer:

see explanation below

Explanation:

Question is incomplete, so in picture 1, you have a sample of this question with the missing data.

Now, in general terms, the absorbance of a substance can be calculated using the beer's law which is the following:

A = εlc

Where:

ε: molar absortivity

l: distance of the light in solution

c: concentration of solution

However, in this case, we have a plot line and a equation for this plot, so all we have to do is replace the given data into the equation and solve for x, which is the concentration.

the equation according to the plot is:

A = 15200c - 0.018

So solving for C for an absorbance of 0.25 is:

0.25 = 15200c - 0.018

0.25 + 0.018 = 15200c

0.268 = 15200c

c = 0.268/15200

c = 1.76x10⁻⁵ M