Chemistry, 16.11.2020 17:20 Terrydactly

.A person is unable to see distinctly the objects placed at large distances but is able to read a book comfortably. Name the defect of vision he is suffering from

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Answer from: alkinoonn

The defect of vision suffered by the person is Myopia

Explanation:

The person can't see farther objects but is able to read a book which is placed closely to the eyes, using these observations the person is suffering from MYOPIA(nearsightedness) in which observer see close objects clearly but farther objects appear blurred.

The light entering the eye isn't correctly bent, the eyeball becomes big , or the eye lens become too converging, which converges the light ray in front of the cornea

This defect can be cured by using concave lenses.

Answer from: Quest

po-215 i got it right on the quiz

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

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