Answer:
the answer is d. 12 protons and no electrons
Explanation:
For Mg atom the atomic number, Z=12
Number of protons in the nucleus = Atomic number of an atom =12
Answer:

Explanation:
Given:
height above which the rock is thrown up, 
initial velocity of projection, 
let the gravity on the other planet be g'
The time taken by the rock to reach the top height on the exoplanet:
where:
final velocity at the top height = 0 
(-ve sign to indicate that acceleration acts opposite to the velocity)

The time taken by the rock to reach the top height on the earth:



Height reached by the rock above the point of throwing on the exoplanet:

where:
final velocity at the top height = 0 


Height reached by the rock above the point of throwing on the earth:



The time taken by the rock to fall from the highest point to the ground on the exoplanet:
(during falling it falls below the cliff)
here:
initial velocity= 0 



Similarly on earth:

Now the required time difference:


The number of protons in any element can never change.
Answer: 20 pm=20*10^-12 m
Explanation: To solve this problem we have to use the relationship given by:
λmin=h*c/e*ΔV= 1240/60000 eV=20 pm
this expression is related with the bremsstrahlung radiation when a flux of energetic electrons are strongly stopped hitting to a catode. The electrons give their kinetic energy to the atoms of the catode.