Final answer:
Ammonium thioglycolate typically has a lower pH than the other relaxers listed, such as sodium hydroxide, which is highly alkaline and thus has a higher pH.
Step-by-step explanation:
Out of the options provided, ammonium thioglycolate, c) typically has a lower pH compared to others such as sodium hydroxide, calcium hydroxide, and thio relaxers. Sodium hydroxide (a) is also known as lye or caustic soda featuring a 1:1:1 ratio of sodium (Na), oxygen (O) and hydrogen (H), and it is highly alkaline meaning its pH is much higher than that of ammonium thioglycolate.
Hair relaxers with a lower pH are usually gentler on the hair and scalp as they do not lift the hair cuticle as much or cause as much swelling as high pH relaxers do.