Answer:
I think it should be about maybe the times of the dinosaurs
also I think 23 to 16 billion years
Explanation:
No explanation sorry if im wrong
The half-life of cobalt-60 is 5.26 years. After 10.52 years, 5 grams of a 20-gram sample will remain is TRUE
<u>Explanation:</u>
Mass of cobalt = 20 g
Half-life = 5.26 years
Mass remains after 10.52 years = 5 g
This can be solved by using given below formula, 
= initial mass
t = number of years from when the mass was m_0
m(t) = remaining mass after t years
Number of half-lives = 
Number of half-lives = 
Number of half-lives = 2
At time zero = 20 g
At first half-life =
= 10 g
At second half life =
= 5 g
The given statement is true.
Molar mass helium gas :
He = 4.0 g/mol
number of moles: 3.75 / 4.0 => 0.9375 moles
1 mole ------ 22.4 ( at STP)
0.9375 ------ ?
volume = 0.9375 x 22.4 / 1
Volume = 21 / 1
Volume = 21 L
hope this helps!
Answer: Bohr proposed his quantized shell model of the atom to explain how electrons can have stable orbits around the nucleus.
so C would seems to be right.
Explanation: The energy of an electron depends on the size of the orbit and is lower for smaller orbits. Radiation can occur only when the electron jumps from one orbit to another. The atom will be completely stable in the state with the smallest orbit, since there is no orbit of lower energy into which the electron can jump.