निम्नलिखित में से कौन सा रासायनिक समीकरण एक संयोजन अभिक्रिया (combination reaction) को दर्शाता है?

Which of the following is an example of a double displacement reaction?

In the thermal decomposition reaction of lead nitrate given below, which compound fills the blank box? 2Pb(NO3)2 (s) → [ ? ] + 4NO2 (g) + O2 (g)

Choose the balanced equation for the following chemical reaction: Hydrogen + Chlorine → Hydrogen Chloride