Question

Which element is a liquid at 758 K and standard pressure?

Answer 1

The answer would be Thallium. This is an element with Tl as its chemical symbol and atomic number 81. This soft gray post-transition steel is not originate free in nature. When inaccessible, thallium look like tin, but tarnishes when unprotected to air.

Answer 2

Answer: option (4) thallium.

Explanation:

1) You have to look at the normal boling and mleting points of the elements.

2) To be liquid the normal melting point must be lower than 758 K and the normal boiling point must be greater than 758 K.

3) The look at the data in a handbook of properties or in internet, and build a table.

4) The given temperature, 758K, is 758 - 273.15 = 484.85 °C.

Element                 Normal melting         Normal boiling        State at 484.85 °C

                               point (°C)                   point (°C)

(1) gold                    1064                           2700                      solid

(2) silver                   961.8                          2162                      solid

(3) platinum             1768                            3825                      solid

(4) thallium               303.5                          1457.8                   liquid

Then, the only element of the choices whose melting point is less than 758 K (484.85) and its boiling point is greater than that, at 1 atm is thallium. So, it is liquid.