Learn Russian: Это лёгкий вопрос.

When это means "this is" or "it is", it stays in this fixed neutral form regardless of the gender of the noun that follows. If you were saying "this question" (as a single phrase without "is"), you would have to use the masculine form этот вопрос.

Why is there no word for "is" in this sentence?

In Russian, the verb "to be" is generally skipped in the present tense. Instead of saying "This is an easy question", you simply put the words together as "This — easy question".

How is the letter г pronounced in лёгкий?

In this specific word, the letter г makes a breathy "kh" sound, similar to a strong English "h". So, лёгкий is pronounced roughly like "lyokh-kiy". This is a special pronunciation exception to the normal hard "g" sound.

Why does лёгкий end in -ий instead of the standard masculine ending -ый?

This happens because of a very important Russian spelling rule. After the letter к (and a few other letters like г, х, ж, ш), you are never allowed to write the letter ы. You must write и instead, which changes the adjective ending from -ый to -ий.