68000 = 6.8 * 10000 = 6.8 * 10^4
hope this helps? c;
Explanation:
The group number in the periodic table represents number of valence electrons of the elements in a certain group.
Group 1 : 2,8,1
Group 2 : 2,8,8,2
Group 3 : 2,8,3
Group 4: 2,4
Group 7 : 2,8,7
Answer:

<em>Sand is a granular material composed of finely divided rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt.</em>
The question is incomplete. Here is the complete question.
An atom of lead has a radius of 154 pm and the average orbitalspeed of the electron in it is about 1.8x
m/s. Calculate the least possible uncertainty in a measurement of the speed of an electron in an atom of lead. Write your answer as a percentage of the average speed, and round it to significant 2 digits.
Answer: v% = 0.21 m/s
Explanation: To calculate the uncertainty, use <u>Heisenberg's Uncertainty Principle</u>, which states that: ΔpΔx≥
where h is <u>Planck's constant</u> and it is equal to 6.626.
m²kg/s.
Since p (momentum) is p = m.v:
mΔv.Δx ≥ 
Δv = 
Given that: r = x = 1.54.
m and mass of an electron is m=9.1.
kg
Δv = 
Δv = 0.0376.
As percentage of average speed:
Δv.
.100% =
.10² = 0.021.10 = 0.21%
The least possible uncertainty in a speed of an electron is 0.21%.