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Answer:
Energy is released.
Explanation:
When an electron absorbs energy, it moves up into an excited state. When it releases energy, it will return to the ground state.
Answer:

Explanation:
Given,
The density of Helium is 
We need to find the density in Dg/μm
We know that,
1 g = 10 dg
1 cm³ = 10¹² μm³
So,

So, the density of Helium is equal to
.
Answer:
90%
Explanation:
Percentage yield = ?
Theoretical yield = 50g
Actual yield = 45g
To calculate the percentage yield of a compound, we'll have to use the formula of percentage yield which is the ratio between the actual yield to theoretical multiplied by 100
Percentage yield = (actual yield / theoretical yield) × 100
Percentage yield = (45 / 50) × 100
Percentage yield = 0.9 × 100
Percentage yield = 90%
The percentage yield of the substance is 90%