trying to fix argument 1 missing or nil? to make object spawn in a 1 out of 150 chance

The above answer is almost right, But you're not checking to see if the selected table entry is nil or not.

Here's my $5 bucks at a stab at this ....

My code:

function Drop() 

    local drops = {"NUKE"} 
    local G = math.random(1, 150) 
    local Selected = drops[G] -- make this a variable, so we can check it in the next step
    if(Selected ~= nil) then -- if its not nil then continue otherwise skip!
        local Obj = game.Lighting:findFirstChild(Selected):Clone() 
        if(Obj ~= nil) then -- make sure theres one available to clone (Might break on the line above)
            Obj.Parent = game.Workspace 
            Obj.Handle.CFrame = script.Parent.Head.CFrame + Vector3.new(4,-3,0)
    --  else
    --      warn("Warning: NUKE is nil!")
        end
    --else
    --  print("Selected[",G,"] = nothing!")
    end
    script:remove()
end 


while true do 
    wait(.1) 
    if (script.Parent.Humanoid.Health <1) then 
        Drop() 
    end 
end

seems to run but rarely lands on the nuke, kinda what you wanted

Hope this helps!

You're problem is here:

local drops = {"NUKE"} 
local G = math.random(1, 150) 
local Obj = game.Lighting:FindFirstChild(drops[G]):Clone()

Currently you try to get a random object, however you only have one object. If it decides to try and grab 132 item in the table, however you do not have 132 or more objects in the table, it'll return nil.

So, what you wanna do is use math.random in a sense of how many you have in the table.

local Drops = {'NUKE'}
local G = math.random(1,#Drops) -- gets between 1 and the amount of drops
if G ~= nil then
    local Obj = game.Lighting:FindFirstChild(Drops[G]:Clone()
end -- check if drops actually has items

Edited version for what you want from the new comment:

local Drops = {'NUKE'}
local G = math.random(1,150) -- gets number between 1 and 150
if G == 1
    local Obj = game.Lighting:FindFirstChild(Drops[1])
    if Obj then
        Obj:Clone().Parent = nil -- change this to your parent
    end -- check for drop
else
    -- not 1, try something else?
end -- check if drops actually has items