Answer:
B. 26amu
Explanation:
The nucleus of an atom in an element contains protons, electrons and neutrons. The proton number equals the electron number in a neutral atom. The proton number is also called the atomic number, denoted by Z.
The mass number also called Atomic mass unit (amu) in this case, of an element is the sum of the proton number and the neutron number in the atom of that element. The mass number is denoted by A.
Hence, A = Z + N
Where A = Mass number
Z = Proton (atomic number)
N = Neutron number
In this question, N is 11 while Z is 15
Hence, the mass number of the element in the question, in AMU, is 15 + 11 = 26amu.
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Answer:
Without an oxygen atmosphere very few things could live on the early Earth. Anaerobic bacteria were probably the first living things on Earth. The early Earth had no oceans and was frequently hit with meteorites and asteroids.
Explanation:
ANSWER
The correct answer is A
<u>EXPLANATION</u>
From the equation 
<u>L.H.S.</u>
Fe = 1
O =2
<u> R.H.S</u>
Fe =2
O =3
Now, let try to balance the oxygen atoms first,
To do this, we know the Least Common Multiples of 2 and 3 is 6
To get 6 atoms of oxygen at L.H.S multiply 2 by 3 and on the R.H.S, multiply 3 by 2
L.H.S.
R.H.S
This means that, 3 should be in front of 
at the L.H.S and 2 should come before 
in the R.H.S of the equation
Now, we have
L.H.S.
Fe = 1
O = 6
<u>R.H.S</u>
Fe =4
O =6
The equation is still not balanced since Fe is not balance
The Least Common Multiple of 1 and 4 is 4
Which means that we need to multiply 1 by 4 at the L.H.S and 4 by 1 at the R.H.S
L.H.S.
R.H.S
We now, have
<u>L.H.S. </u>
Fe= 4
O=6
<u>R.H.S</u>
Fe =4
O=6
Hence the balanced equation is
