Question

a person hears an echo from the top of a tower 2.2 seconds after the second is produced how far away it's the lowest from the person? speed of the sound in air is 332 metre per second (a) what was the Helium has zero valency (b) name the scientist and his experiment to prove the molecules of an atom is positively charged

Answer 1

Time , t = 2.2 sec
Speed , v = 332 m/s

2d = v × t

2 d = 332 × 2.2
2 d = 730.4
d = $\frac{730.4}{2}$
= 365.2 metres

The distance of the person from the tower is 365.2 metres.
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=>Helium's atomic no: is 2.
=>The no : of protons and electrons is also 2.
=>The electronic configuration is 2 ,0
=>As it does not need to share , give or lose electrons its valency is 0.
=>The electrons in its valence shell is also 0.
=>Therefore , its valency is 0.
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Rutherford is the scientist who proved that the centre of an atom is positively charged in his gold foil experiment

Answer 2

Given,

Time = 2.2seconds

Speed of sound = 332m/s

Let's think the distance is 2d

Now,

Speed = Distance / time

or, Distance = Time × Speed

or, 2d = 2.2 × 332

or,d = 730.4/2

or, d = 365.2m

The distance of the person from the tower is 365.2m

2))Why hellium has 0 Vacancy
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We know that Vacancy tells us the number of electrons needed to get a stable form.Helium is already a stable element .As the configuration of Helium is 1s2 and the maximum capacity of S shell is 2.

So Helium doesn't need to loose or gain electrons to get a stable form.

3)The name of the Scientist is Rutherford and the famous experiment was 'Gold foil Experiment'

Hope it helps.