Answer : The type of reaction described in the sentence is Synthesis or Combination
Explanation :
The balanced equation for the reaction between Phosphorous and Oxygen gas can be written as

From the above equation we can see that there are two different reactants ( P and O₂ ) which are combining with each other to give a single product.
This type of reaction is known as Combination or Synthesis.
A general form of Synthesis reaction is given below.

Here we can conclude that a synthesis / combination reaction is the one where 2 or more reactants combine together to give only one product .
Answer:
Kinetic energy: 
Velocity: 
Explanation:
From the equations of the photo-electric effect,
We know:

Where,
1.
is the Planck's constant which is 
2.
are the frequency of light emitted and threshold frequencies respectively.
3.
is the kinetic energy of the electrons emitted.
By fact, we come to know that the threshold frequency of Zn is 300nm
And also
Where ,
1.
is the speed of light 
2.
is the wavelength.
Thus,

Now to find velocity:

Answer:
No of neutrons and protons decides mass of the atom. Electrons having negligible
mass are ignored.
Mass of atom
Mass of atom= sum of no of protons(Z) and neutons(N)
=Z+N
For eg:
In hydrogen atom,
Mass of H= Z+N
=1+0
=1 AMU
Answer:
atoms of C? 2.25 x 1022 atoms C x 1 mole C = 0.037 mol C
Explanation:
How many moles of C are in 2.25 x 1022 atoms of C?