What is the $H_{3}O^{+}$ ion called?

According to the Arrhenius theory,which ion is produced when a base ionizes in water?

What happens when a solution of an acid is mixed with a solution of a base in a test tube?
$(i)$ The temperature of the solution increases
$(ii)$ The temperature of the solution decreases
$(iii)$ The temperature of the solution remains the same
$(iv)$ Salt formation takes place

If the concentration of hydronium ions in an aqueous solution is $[H_3O^+] = 10^{-5} \; M$,what is the $pOH$ of the solution?

For making cake,baking powder is used. If at home your mother uses baking soda instead of baking powder in the cake,
$(a)$ how will it affect the taste of the cake and why?
$(b)$ how can baking soda be converted into baking powder?
$(c)$ what is the role of tartaric acid added to baking soda?

$A$ sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the $pH$ paper yellowish-orange. Which of the following would change the colour of this $pH$ paper to greenish-blue?