Can we make more than two cells in a row with only one use of <tr> ?

Yes, just put more columns. <table> <tr> <td>One</td> <td>Two</td> <td>Three</td> </tr> </table>

it's your wish. you can make as many as you want

You can use rowspan to achieve it!

yes you can add more than 2 cells. Cells are added using <td> tag and you may add as many of them as you require. structure might be <table> <tr> <td> cell 01 </td> <td> cell 02 </td> <td> cell 03 </td> <td> cell 04 </td> </tr> </table>