instructions: in each question, list the elements from least to greatest reactivity:
5) copper (cu), manganese (mn), rubidium (rb)
6) phosphorus (p), oxygen (o), nitrogen (n)
7) magnesium (mg), potassium (k), beryllium (be)
8) bromine (br), chlorine (cl), iodine (i)

Question

Accepted Answer

# Explanation:
## Step1: Determine reactivity for metals
For metals, reactivity increases down a group and across a period (left - to - right for some trends). Rubidium (Rb) is an alkali metal (Group 1), manganese (Mn) is a transition metal, and copper (Cu) is also a transition metal. Alkali metals are highly reactive. Among transition metals, Mn is more reactive than Cu. So for 5) $Cu<Mn<Rb$.
## Step2: Determine reactivity for non - metals (p - block elements)
For non - metals in the p - block (Groups 15 - 17), reactivity (for non - metals like in the case of forming compounds) has some trends. Nitrogen ($N$) has a triple bond ($N\equiv N$) which is very stable. Oxygen ($O$) is more reactive than nitrogen (forms many oxides). Phosphorus ($P$) is more reactive than nitrogen (e.g., forms $P_4O_{10}$ easily). So for 6) $N<P<O$.
## Step3: Determine reactivity for metals (Group 2 and Group 1)
Potassium ($K$) is an alkali metal (Group 1), magnesium ($Mg$) is Group 2, and beryllium ($Be$) is Group 2. Alkali metals are more reactive than Group 2 metals. Among Group 2 metals, reactivity increases down the group ($Be<Mg$). So for 7) $Be<Mg<K$.
## Step4: Determine reactivity for halogens
For halogens (Group 17), reactivity decreases down the group. Chlorine ($Cl$) is above bromine ($Br$), and bromine is above iodine ($I$). So for 8) $I<Br<Cl$.

# Answer:
5) $Cu<Mn<Rb$
6) $N<P<O$
7) $Be<Mg<K$
8) $I<Br<Cl$

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QUESTION IMAGE

Question

Explanation:

Step1: Determine reactivity for metals

Step2: Determine reactivity for non - metals (p - block elements)

Step3: Determine reactivity for metals (Group 2 and Group 1)

Step4: Determine reactivity for halogens

Answer: