$A$ light year is a unit of which physical quantity? Time or distance?

What is $1$ radian? What is $1$ steradian?

$1\,J =$ ............ $\text{calorie}$. (Fill in the blank)

Length cannot be measured by

Fill in the blanks:
$(a)$ $1 \, rad = \dots \text{ degrees}$
$(b)$ Light year is a unit of $\dots$
$(c)$ The solid angle subtended by a hemisphere at its center is $\dots$

What is a physical quantity? Write its types.