Why am I getting an error saying unhashable list?

This is the code that I’m running on PyCharm and keep getting an error saying if form in exceptions:
TypeError: unhashable type: ‘list’. I am new to python. Kindly help me out

        import matplotlib.pyplot as plt
        import pandas as pd
        import nltk
        
        data=pd.read_excel(r"C:\Users\amgup\Downloads\classification\Model_Dataset.xlsx", usecols=['Category','Title','Description'])
        
        # Combining title and description into one column
        data['combined']= (data['Title']+' '+data['Description']).str.lower()
        data=data.drop(columns=['Title','Description'])
        print(data)
        
        # shuffling the order of the rows. sample() returns random rows from the data and frac specifies what fraction has to be returned
        # frac=1 means the entire data in a random order
        data=data.sample(frac=1)
        print(data)
        
        # Counting the numnber of times each category has appeared
        count=data['Category'].value_counts()
        print(count)
        
        # Creating a barplot of the count
        bar_plot=plt.barh(count.keys(),count.values)
        plt.savefig(r"C:\Users\amgup\Downloads\classification\barplot_of_categories.png")
        
        y=list(data['combined'])
        print(y)
        
        #lemmatization
        from nltk.corpus import stopwords
        nltk.download('stopwords')
        stop_words = set(stopwords.words('english'))
        tokens=[]
        from nltk.stem import WordNetLemmatizer
        nltk.download('wordnet')
        lemmatizer = WordNetLemmatizer()
        for x in y:
            x = str(x)
            x = x.lower()
            x = x.split()
            x = [lemmatizer.lemmatize(x) for word in x if word not in stop_words]
            x = ' '.join(x)
            tokens.append(x)
        print(tokens)

>Solution :

x = x.split() turns your string x into the list.

In your comprehension, you should put lemmatizer.lemmatize(word) instead of lemmatize(x)

You are looping through the words in x x and you want to do transformation on each word