What's the meaning of adding numbers before element symbols in chemical equations For example, 2mg + O2 ignites 2 before mg in "2MgO"

What's the meaning of adding numbers before element symbols in chemical equations For example, 2mg + O2 ignites 2 before mg in "2MgO"

It means that two units, such as Mg, means that two Mg atoms and one oxygen molecule just completely react. If there is more mg than enough, the surplus of O2 is just the reflection, that is, the proportion of the reflection

The meaning of these chemical symbols!
The meaning of Chemistry: Fe2O3 FeS2 FeCO3 CuFeS2 Cu2S
What is the meaning of it?

Fe2O3, iron oxide,
FeS2, FeS2,
FeCO3, ferrous carbonate,
CuFeS2, ferrous copper sulfide,
Cu2S cuprous sulfide

Find the rule and add operation symbol bracket
1/2 3/4 9/8 27/16 （ ）（ ）
1/6 1/6 1/6 1/6=3

1 / 2 3 / 4 9 / 8 27 / 16 (81 / 32) (243 / 64)
（1/6 +1/6 + 1/6 ）/ 1/6=3

How does the equation of one variable change when the bracket sign is removed?

If there is a positive sign before the bracket, the sign in the bracket will remain unchanged. If there is a negative sign before the bracket, the sign in the bracket will be reversed

What is the change of the symbol after a - (- a-b) is removed?
It's mainly about how to change the - A in brackets

You remember a rule: the negative sign is in front of the bracket, and the sign inside the bracket should be changed. So - A becomes + A. I hope it will help you

What's the change of the sign after (- a-b) removing the brackets?

(- a-b) the sign does not change after the brackets are removed,
But it must be written as the following canonical expression
-（a+b)

Fill in the appropriate sign or bracket for - 1 5 = 24 to make the equation true
You can't change the order

（-1/5+5）* 5 =24

12 () 11 () 11 = 24 what symbols should be filled in the three brackets to make the equation hold

12×(11+11)÷11=24

What operation symbol should be filled in the middle of 4 = 2

4/4+4/4=2
4*4/(4+4)=2
(4/(4+4))*4=2
4/((4+4)/4)=2

Fill in the middle of 16 2 operation symbols (brackets can also be used) and finally equal to 1992
At least two

1992=2000-8
=16*125-8
=16*（124+1）-8
=2*2*2*2*（2*2*2*2*2*2*2+2/2）-2*2*2