What is the melting point of the substance represented by the complete heating curve below? a line graph showing the heating curve of a substance being heated from the solid phase all the way to the gas phase. the substance starts at a temperature around 0°c and ends at a temperature around 70°c. first, there is an incline with a positive slope from 0°c to 20°c, followed by a horizontal region at 20°c. then there is another incline with a positive slope from 20°c to 60°c, followed by another horizontal region at 60°c. the end of the heating curve shows another incline with a positive slope from 60°c to 70°c.
a. 0°c
b. 20°c
c. 40°c
d. 60°c

option B. 20°C.

Explanation:

1. The melting point is the temperature at which a substance changes from solid to liquid.

2. The phase changes, e.g. melting, boiling, freezing, and condensation, happen at constant temperature.

3. In a temperature vs time diagram, a horizontal (flat) line represents constant temperature.

4. In a temperature vs time diagram, the phases from left to right go from solid to liquid to gas.

4. Hence, the first horizontal  region at 20°C is indicating the constant temperature at which the substance is changing from solid to liquid (melting).

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

it means there are 3 atoms of oxygen