How would I condense these if statements?

You could use tables or use the "var" variable, both works, but the reason that your script doesn't work is probably because you never defined the "var" variable, that means that the script thinks "var" is equal to nil (nothing). So you're basically checking

if (nil == 1) then

You can define the variable. Also to avoid repeating the if statement and module requiring, you COULD use a table, but if you want to have a name like "module1", "module2" "module10" etc, you can concatenate strings to find the name of the module to find, concatenation is a way to connect two strings together. It's supposed to be a "..", For example,

local a = "Hello"
local b = "Roblox"

print(a..b) -- You're basically connecting two strings together, this will print "HelloRoblox" because you connected "Hello" (a) with "Roblox" (b)

print(a.." "..b) -- This will print "Hello World" because you connected Hello (a) with a space and connected that with "Roblox"

You could find the module using this

local moduleName = "module"..var -- This will "module1" if var = 1 and "module10" if var = 10

Here is the full script

local var = 1

local function onInputBegan(inputObject, gameProcessedEvent)
	if gameProcessedEvent then return end
	if inputObject.KeyCode.Name == "F" then
		local moduleName = "module"..tostring(var) -- We turn var into a string because it's a number and not a string
		if (game.ReplicatedStorage:FindFirstChild(moduleName) and game.ReplicatedStorage:FindFirstChild(moduleName):IsA("ModuleScript")) then
			-- We check if the module exists and it's a modulescript and not a part or script
			require(game.ReplicatedStorage[moduleName]) -- Using game.ReplicatedStorage[] is the same as game.ReplicatedStorage.
		end
	end
end

If you wanted to, you could still use an array for this.

An array is basically a table which can hold any values. Arrays have to be indexed using a number. For example

-- Indexes start at 1
local fruits = {
	"Oranges", -- Index 1
	"Apples", -- Index 2
	"Mangoes", -- Index 3
}

print(fruits[1]) -- This will print "Oranges" because "Oranges" is at index 1

fruits[1] = "Tomato" -- We replace first index (Oranges) with "Tomato"

print(fruits[1]) -- This will print "Tomato"

We can also use the "#" symbol to get the amount of keys in the array. For example

local a = {"A", "B"}

print(#a) -- This will print 2 because there are two keys ("A" and "B")

a[#a + 1] = "C" -- Saying #a + 1 is basically saying the next index after the last index, this will not override any keys, this will create a new index at the end of the table

print(#a) -- this will print 3 now

Since your "var" variable is a number, it can be used as an index. This is your script with a table

local var = 1

local modules = { -- These have to be in order, because we are gonna be using index for this
	game.ReplicatedStorage.module1,
	game.ReplicatedStorage.module2,
	game.ReplicatedStorage.module2
}

local function onInputBegan(inputObject, gameProcessedEvent)
	if gameProcessedEvent then return end
	if inputObject.KeyCode.Name == "F" then
		local module = modules[var] -- Getting the module using index
		if (module and module:IsA("ModuleScript")) then -- If module is not equal to nil (doesn't exist) and it's a module script then
			require(module)
		end
	end
end