How to express your answer as an integer?

(a) W

(b) X

(c) Y

Explanation:

Let's consider the following table with melting and boiling points for 4 substances.

Substance     Melting Point (°C)       Boiling Point (°C)

     W                       -7                                  60

     X                       660                              2500

     Y                        180                               1330

     Z                         115                                445

Let's consider that:

(a) Which substance is a gas at 100°C?

At 100 °C, W is above the boiling point

(b) Which substance is a liquid for the largest range of temperature?

The largest difference between the melting point and the boiling point is that of X: 2500 - 660 = 1840.

(c) Which substance is liquid at 1000 °C and a gas at 2000°C?​

Y is between the melting and the boiling point at 1000 °C and above the boiling point at 2000 °C.