noble_gas.rb

class Element
  attr_accessor :name, :symbol, :number
  
  def initialize(name, symbol, number)
    self.name = name
    self.symbol = symbol
    self.number = number
  end
  
  def describe
    puts "#{self.name} (#{self.symbol}) has atomic number #{self.number}."
  end
end

class NobleGas < Element
  attr_accessor :category, :type, :reactivity
  
  def initialize(name, symbol, number)
    super(name, symbol, number)
    
    self.category = "gas"
    self.type = "noble gas"
    self.reactivity = "low"
  end
  
  def describe
    puts "#{self.name} (#{self.symbol}; #{self.number}) is a #{self.category} " +
         "of type #{self.type}. It has #{self.reactivity} reactivity."
  end
end

argon = NobleGas.new("Argon", "Ar", 18)
argon.describe