Can an element have both an id and a class?

I would like to add that if you add both ID and a class that contradict each other, the ID will have higher priority.

For example:

CSS:

.par_color{
    color:red;
}

#par_color{
    color:blue;
}

HTML:

<section id="par_color" class="par_color">Some txt</section>

Some txt string will be shown in blue and not in red.

Yes, an element can have one ID (which must be unique!) and multiple classes at the same time. To have multiple classes, use a space between them, here's an example:

<div id="myID" class="class1 class2 class3">Content</div>

Yes. Self explanatory.

Additionally, it's common to have more than one class IE -

<div class="oneClass andAnother"></div>

but only one ID per element, and each ID should only be used once per HTML page.