I just started out with mods, and I was trying to make some basic items. I got the items to load into the game but I cannot figure out what is wrong with the textures and why they are not loading. I checked the folder structure and the contents of the json files more than 5 times and I could not find anything misplaced or mistyped. I would greatly appreciate any help.
Items class

package com.raresamza.firstmod.item;


import com.raresamza.firstmod.FirstMod;

import net.minecraft.world.item.Item;
import net.minecraftforge.eventbus.api.IEventBus;
import net.minecraftforge.registries.DeferredRegister;
import net.minecraftforge.registries.ForgeRegistries;
import net.minecraftforge.registries.RegistryObject;

import static com.raresamza.firstmod.item.ModCustomCreativeTab.*;

public class ModItems {

    public static final DeferredRegister<Item> ITEMS=DeferredRegister.create(ForgeRegistries.ITEMS, FirstMod.MOD_ID);
    public static final RegistryObject<Item> PLUTONIUM = addToTab(ITEMS.register
            ("plutonium",
                    ()->new Item(new Item.Properties().stacksTo(32))));

    public static final RegistryObject<Item> RAW_PLUTONIUM = addToTab(ITEMS.register
            ("raw_plutonium",
                    ()->new Item(new Item.Properties().stacksTo(32))));

    public static final RegistryObject<Item> ZIRCON = ITEMS.register("zircon",
            () -> new Item(new Item.Properties()));
    public static final RegistryObject<Item> RAW_ZIRCON = ITEMS.register("raw_zircon",
            () -> new Item(new Item.Properties()));


    public static void register(IEventBus eventBus) {
        ITEMS.register(eventBus);
    }
}

Custom creative tab
 

package com.raresamza.firstmod.item;

import com.raresamza.firstmod.FirstMod;
import net.minecraft.core.registries.Registries;
import net.minecraft.network.chat.Component;
import net.minecraft.world.item.*;
import net.minecraft.world.level.ItemLike;
import net.minecraftforge.api.distmarker.Dist;
import net.minecraftforge.event.BuildCreativeModeTabContentsEvent;
import net.minecraftforge.eventbus.api.SubscribeEvent;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.registries.DeferredRegister;
import net.minecraftforge.registries.RegistryObject;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Supplier;

@Mod.EventBusSubscriber(modid = FirstMod.MOD_ID,bus = Mod.EventBusSubscriber.Bus.MOD,value = Dist.CLIENT)
public class ModCustomCreativeTab {
    public static final DeferredRegister<CreativeModeTab> TABS=DeferredRegister.create(Registries.CREATIVE_MODE_TAB, FirstMod.MOD_ID);
    public static final List<Supplier<?extends ItemLike>> MOD_TAB_ITEMS=new ArrayList<>();

    public static final RegistryObject<CreativeModeTab> SPECIAL_TAB=TABS.register("modtab",
            ()-> CreativeModeTab.builder()
                    .title(Component.translatable("itemGroup.modtab"))
                    .icon(ModItems.PLUTONIUM.get()::getDefaultInstance)
                    .displayItems((displayParams,output)->
                        MOD_TAB_ITEMS.forEach(itemLike -> output.accept(itemLike.get())))
                    .build());

    public static <T extends Item> RegistryObject<T> addToTab(RegistryObject<T> itemLike) {
        MOD_TAB_ITEMS.add(itemLike);
        return itemLike;
    }

    @SubscribeEvent
    public static void buildContents(BuildCreativeModeTabContentsEvent event) {
        if(event.getTabKey()== CreativeModeTabs.BUILDING_BLOCKS) {
            event.accept(ModItems.PLUTONIUM);
            event.accept(ModItems.RAW_PLUTONIUM);
            event.accept(ModItems.ZIRCON);
            event.accept(ModItems.RAW_ZIRCON);
        }
        if(event.getTab()==SPECIAL_TAB.get()) {
            event.accept(Items.APPLE);
            event.accept(ModItems.PLUTONIUM);
            event.accept(ModItems.RAW_PLUTONIUM);
            event.accept(ModItems.ZIRCON);
            event.accept(ModItems.RAW_ZIRCON);
        }
    }
}

raw_plutonium.json

{
  "parent": "minecraft:item/generated",
  "textures": {
    "layer0": "firstmod:item/raw_plutonium"
  }
}

plutonium.json

{
  "parent": "minecraft:item/generated",
  "textures": {
    "layer0": "firstmod:item/plutonium"
  }
}

I would like to include a screenshot of the resource folder structure in case I might have somehow misplaced something but I couldn't find how to paste the image. Also, I have read other threads on this but it did not help, couldn't find anything wrong with my code.

Your textures path should be for example resources/assets/firstmod/textures/item/plutonium.png

and your mod id must be firstmod

Just now, Zacomat said:

Your textures path should be for example resources/assets/firstmod/textures/item/plutonium.png

and your mod id must be firstmod

the mod id is firstmod and the folder structure is the same as the one you have mentioned

 

Are you sure "layer0" points to a valid item texture? If a json item model doesn't use an existing image file for it's texture(s), then it will have the purple and black checkerboard texture.