It is true because it just is
Explanation:
1) from the periodic table for example if u looking for K it is from the group 1A so the valancey = +1 that is mean it loses one electron to reach a stable state. and this applied for the 1A , 2A, 3A groups.
if u looking for N it is from group 5A so its valency is -3
so it gain 3 electrons to reach a stable state to complete its orbital to 8 electrons. this applied to 5A, 6A,7A
for the transition metals and simimetals other rules.
2) neutral if the element does not hold any charge like
H2, O2, N2, Fe, Au, Cu ...
isotope : if the 2 elements have same symbol and atomic number but they differ in the mass number because the have different numbers of neutrons.
if the element is charged then it is considered as an ion ex: Fe2+ then it is iron cation ( +ion)
F- then it is fluoride anion (-ion)
if u have any doubt just writ a comment ( ;
Answer:

Explanation:
First reaction gives you the number of moles or the mass from Carbon and hydrogen
for carbon:


Analogously for hydrogen:
0.0310g
have 0.0034gH or 0.0034mol of H
In the second reaction you can obtain the amount of nitrogen as a percentage and find the mass of N in the first sample.

now

this is equivalet to 0.002mol of N
with this information you can find the mass of oxygen by matter conservation.

this is equivalent to 0.004molO
finally you divide all moles obtained between the smaller number of mole (this is mol of H)

and you can multiply by 5 to obtain: 
Answer:
H2SO4 + 8HI → H2S + 4I2 + 4H2O
Answer: Either A or D
Geologists and paleontologists constructed the geologic table based on the relative positions of different strata and fossils, and estimated the time scales based on studying rates of various kinds of weathering, erosion, sedimentation, and lithification.