Consider a data structure like a $1$D array that is being written and read by multiple threads at

the same time. Should this data structure be guarded by a mutex?

Yes$-$it will cause the program to use less memory.

$$ Yes $-$ it prevents race conditions from occurring when multiple threads use the same index.

No $-$it will only slow down the program.

No $-$if there is only one array, the OS will only allow one thread to write to it anyway.