POSIX Pthread, Semaphore and Mutex ID Question

Hi, I am trying to figure out the ID value when thread, sem or mutex is not present. Which value does the ID take, 0 or NULL?

What do you mean by ID here? Do you want to ask what to initialize a mutex handle to? If so, you can use NULL -

SemaphoreHandle_t xMutex = NULL;
xMutex = xSemaphoreCreateMutex();

if( xMutex != NULL )
    /* Use mutex. */

My question is when I declare xMutex without giving a value like this:

SemaphoreHandle_t xMutex;

What is the value of xMutex initially?

If it’s a global or static variable it’s zero initialized i.e. NULL following the C standard.
That’s not directly related to FreeRTOS.