How to combine IF OR functions

[JD2170]

So I want to do the following:

1 cel has a dropdown of 3 items

in another cell I want to say: 

if option A then 1 comes out

if option B then 2 comes out

if option 3 then 3 comes out

How do I fix this please. Thanks

[#2]

@JD2170 

Like this:

The formula in B2 is

=MATCH(A2,$H$2:$H$4,0)

[#3]

My source of the dropdown is in another worksheet same workbook
Worksheet A: 

2MER010101Kwalitatiefgroenversterkthetdistrict	5074000000
2MER010102Sliminvestereninhetopenbaardomein	5072500000
2MER010103Sportenspelzijngeïntegreerdinhetopenbaardomein	5071000000

This I want to combine in worksheet B

Doelstelling	Bpl

Where "doelstelling has the dropdown of the first colums (2MER....) and the Bpl has then the option which is 1:1 (so if they choose 2MER010101 then the option "5074000000" comes out; so on)

I've tried your solutions but they daon't work for me. Thanks for the info

[#4]

@JD2170 

Let's say the source is B2:B4 on a sheet named Source Data.

The formula from my previous example then becomes

=MATCH(A2,'Source Data'!$B$2:$B$4,0)

[#5]

@JD2170 

A newer function that replaced MATCH in 365:

= XMATCH(selected, validationList)

The 'exact match' is now the default.  The defined names can be chosen according to the context.