Which attribute is not essential under <iframe>?
a) src
b) height
c) width
d) frameborder

Answer: d
Explanation: An iframe is equivalent to a window that has been cut into our page, it is created using <iframe> element. Src, height, width attribute are essentially used inside of this. Src attribute specifies the URL of the page which is to be shown. Height and width specify the height and width of an iframe in pixels.